Decision tree scoring system to guide selection for consumer preference in sweetpotato breeding trials

BACKGROUND

Previously, a lexicon and protocol for quantitative descriptive analysis (QDA) was established for the Uganda sweetpotato breeding program. The implication of QDA scores for priority sensory attributes on consumer preference should be determined to interpret results efficiently and make decisions effectively. The present study aimed to develop a gender-responsive decision tree to obtain an overall sweetpotato eating quality score to facilitate demand-led targeted breeding selection. It focused on Kamuli and Hoima districts (Uganda) and uses pre-lease advanced clones ('NKB3', 'NKB105', 'NKB135', 'D11' and 'D20'), released varieties ('NASPOT 8' and 'NAROSPOT 1') and landraces ('Muwulu-Aduduma', 'Umbrella').

RESULTS

Including boiled sweetpotato sensory characteristics, namely mealy, sweet taste, sweetpotato smell, firm and not fibrous, in breeding design would benefit end-users, especially women given their role in varietal selection, food preparation and marketing. 'D20', 'NASPOT 8' and 'NAROSPOT 1' were most liked in both districts. 'NKB3' and 'D11' were the least liked in Hoima, whereas 'Muwulu-Aduduma' was the least liked in Kamuli. There was a positive correlation between color and overall liking (r2 = 0.8) and consumers liked the color (average rating ≥ 6 on a nine-point hedonic scale) of all genotypes. Threshold values (average rating on 11-point scales) for consumer acceptability were identified (sweet taste = 6, sweetpotato aroma and flavor = 6, firmness = 3, and mealiness = 4). A regression decision tree tool was created to calculate an eating quality selection index when screening lines in breeding programs using the values.

CONCLUSION

Decision trees that include consumer needs and gender considerations would facilitate demand-led breeding and make varietal selection in sweetpotato breeding programs more effective. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Baked sweetpotato textures and sweetness: An investigation into relationships between physicochemical and cooked attributes

Sweetpotato varieties vary greatly in perceived textures and sweetness. This study identified physicochemical factors that influence these attributes in cooked sweetpotatoes. Fifteen genotypes grown on three plots were baked and evaluated by a trained descriptive sensory analysis panel for sweetness and 13 texture attributes. Mechanical parameters were measured by texture profile analysis (TPA); and composition (starch, cell wall material, sugar contents), starch properties (thermal, granule type ratios, granule sizes), and amylase activities were characterized. TPA predicted fracturability and firmness well, whereas starch and sugar contents, B-type starch granule ratio, and amylase activities influenced prediction of mouthfeel textures. Sweetness perception was influenced by perceived particle size and sugar contents; and maltose generation during baking was highly correlated with raw sweetpotato starch content. These relationships between physicochemical sweetpotato properties and baked textures and sweetness could benefit breeders and processors in selecting biochemical traits that result in consumer preferred products.

Biomarkers of Metabolic Adaptation to High Dietary Fats in a Mouse Model of Obesity Resistance

Obesity-resistant (non-responder, NR) phenotypes that exhibit reduced susceptibility to developing obesity despite being exposed to high dietary fat are crucial in exploring the metabolic responses that protect against obesity. Although several efforts have been made to study them in mice and humans, the individual protective mechanisms are poorly understood. In this exploratory study, we used a polygenic C57BL/6J mouse model of diet-induced obesity to show that NR mice developed healthier fat/lean body mass ratios (0.43 ± 0.05) versus the obesity-prone (super-responder, SR) phenotypes (0.69 ± 0.07, p < 0.0001) by upregulating gene expression networks that promote the accumulation of type 2a, fast-twitch, oxidative muscle tissues. This was achieved in part by a metabolic adaptation in the form of blood glucose sparing, thus aggravating glucose tolerance. Resistance to obesity in NR mice was associated with 4.9-fold upregulated mitoferrin 1 (Slc25a37), an essential mitochondrial iron importer. SR mice also showed fecal volatile metabolite signatures of enhanced short-chain fatty acid metabolism, including increases in detrimental methyl formate and ethyl propionate, and these effects were reversed in NR mice. Continued research into obesity-resistant phenotypes can offer valuable insights into the underlying mechanisms of obesity and metabolic health, potentially leading to more personalized and effective approaches for managing weight and related health issues.

A sensory lexicon to characterize the quality of fresh and preserved peppers

Pepper fruits (Capsicum annuum) are economically important commodities worldwide due to their unique sensory profiles and rich antioxidant properties. With ongoing research efforts in optimizing the production and processing of peppers, there is a need for a standardized tool to evaluate the quality of peppers and pepper products. The objective of this work was to develop a sensory lexicon to characterize fresh and preserved peppers. A panel of 10 volunteers was recruited and trained in quantitative descriptive sensory analysis for a total of 37 h. Commercially available fresh, pickled, and roasted peppers were used to establish definitions, methods of evaluation, and reference materials for each unique attribute; and attribute intensities were scored on a scale ranging from 0 to 15. Commercially available fresh and preserved pepper samples (n = 22) were evaluated by the panel in duplicate to validate the lexicon. Principal component analysis was used to visualize differences among the products, and attribute redundancies were evaluated through analysis of correlations. This lexicon with 46 clearly defined terms that describe fresh, pickled, and roasted pepper products is comprised of 14 aroma, 19 flavor, 9 texture, and 4 chemesthetic attributes. Smoky, burnt, and cooked tomato flavors were typical of roasted red bell peppers, while the floral attribute was characteristic of fresh red bell peppers, and vinegar, pungency, and spicy notes characterized pickled peppers. The lexicon enabled the characterization and differentiation of a wide range of pepper products and lays the framework for quality evaluation and product improvement. PRACTICAL APPLICATION: Breeders and processors are seeking technologies that ensure desirable quality of fresh and processed peppers for an extended shelf life. This sensory lexicon comprised of 14 aroma, 19 flavor, 9 texture, and 4 chemesthetic attributes serves as a basis for evaluating various strategies toward quality improvement, such as novel processing of pepper products.

Levilactobacillus brevis, autochthonous to cucumber fermentation, is unable to utilize citric acid and encodes for a putative 1,2-propanediol utilization microcompartment

The metabolic versatility of Levilactobacillus brevis, a heterofermentative lactic acid bacterium, could benefit environmentally compatible and low salt cucumber fermentation. The biodiversity of Lvb. brevis autochthonous to cucumber fermentation was studied using genotypic and phenotypic analyses to identify unique adjunct cultures. A group of 131 isolates autochthonous to industrial fermentations was screened using rep-PCR-(GTG)5 and a fermentation ability assay under varied combinations of salt (0 or 6%), initial pH (4.0 or 5.2), and temperature (15 or 30°C). No apparent similarities were observed among the seven and nine clusters in the genotypic and phenotypic dendrograms, respectively. A total of 14 isolates representing the observed biodiversity were subjected to comparative genome analysis. The autochthonous Lvb. brevis clustered apart from allochthonous isolates, as their genomes lack templates for citrate lyase, several putative hypothetical proteins, and some plasmid- and phage-associated proteins. Four and two representative autochthonous and allochthonous Lvb. brevis, respectively, were subjected to phenotype microarray analysis using an Omnilog. Growth of all Lvb. brevis strains was supported to various levels by glucose, fructose, gentiobiose, 1,2-propanediol, and propionic acid, whereas the allochthonous isolate ATCC14890 was unique in utilizing citric acid. All the Lvb. brevis genomes encode for 1,2-propanediol utilization microcompartments. This study identified a unique Lvb. brevis strain, autochthonous to cucumber, as a potential functional adjunct culture for commercial fermentation that is distinct in metabolic activities from allochthonous isolates of the same species.

Prevention of microbes-induced spoilage in sodium chloride-free cucumber fermentations employing preservatives

This study evaluated preservatives to stabilize sodium chloride (NaCl)-free-cucumber fermentations. The brining of air-purged laboratory cucumber fermentations with 100.0 mM calcium chloride (CaCl₂ ) and 25.0 mM acetic acid resulted in immediate rises in pH, the chemical reduction of the medium, and malodors. Supplementation with 3.0 mM sodium benzoate or 3.0 mM potassium sorbate enabled a decline in pH, a continuous oxidative state of the medium, and delayed rising pH spoilage. However, lactic and acetic acids eventually disappeared in fermentations supplemented with preservatives. The amount of preservatives needed to suppress growth of brined-cucumber-spoilage microbes was determined in Fermented Cucumber Juice Medium (FCJM). Supplementation of FCJM with 10.0 mM sodium benzoate was inhibitory for the spoilage yeasts, Issatchenkia occidentalis and Pichia manshurica, and the lactobacilli, Lentilactobacillus buchneri and Lentilactobacillus parafarraginis, but not of Zygosaccharomyces globiformis. Potassium sorbate inhibited the spoilage yeasts at 15.0 mM in FCJM but not the lactobacilli. Supplementation of FCJM with 20.0 mM fumaric acid had a bactericidal effect on the spoilage-associated lactobacilli. As expected, NaCl-free-commercial cucumber fermentations brined with 100 mM CaCl₂ , no acetic acid, and 6 mM potassium sorbate resulted in complete fermentations, but supported rising pH, microbially induced spoilage during long-term storage. Post-fermentation supplementation with 12 mM sodium benzoate, 10 mM fumaric acid, a combination of the two, or 10 mM fumaric acid and 2 mM AITC prevented microbial activity during long-term bulk storage. PRACTICAL APPLICATION: Several preservative-based strategies for stabilizing NaCl-free cucumber fermentation in a commercial production setting were developed, enabling the implementation of a processing technology that reduces wastewater volumes and environmental impact.

Sweetpotato chip texture and fat content: Effects of enzymatic modification of cell wall polymers

Impacts of cell wall polymers on sweetpotato chip texture and fat content were investigated through enzymatic modification. Covington sweetpotato slices were treated with cellulase, hemicellulase, pectinase, pectin methyl esterase, protease, the enzyme blend Viscozyme, or no enzymes (control) at 40-45°C for 0.5-2 h. Treated slices were blanched, dried, and fried in triplicate per experimental condition. Breaking forces of 20 chips per frying replicate were measured followed by chip fat, moisture, sugar, alcohol insoluble solids, glass transition temperature, and color analyses. Untreated slices from each batch (daily check) were fried and analyzed to account for starting material variability. Viscozyme and protease-treated chips had the greatest reduction in breaking force from untreated chips (-30.9% and -23.7%, respectively), while pectin methyl esterase-treated chips had the lowest reduction in breaking force (-9.0%). Chips treated with Viscozyme for 2 h were 6.7-6.3 percentiles lower in fat than the control. Principal component analysis elucidated that chip breaking force was associated with unfried slice puncture force, alcohol insoluble solids, and chip color, and chip fat content was inversely associated with maltose content and glass transition temperature. Breaking down multiple cell wall polysaccharides or structural proteins weakened chip textures, while strengthening the pectic fraction resulted in harder chips. Chip fat reduction also occurred when multiple cell wall polysaccharides were broken down. Therefore, cell wall polymers impact sweetpotato chip texture and fat contents, and their attributes should be considered when selecting cultivars and processes for sweetpotato chips. PRACTICAL APPLICATION: Sweetpotato chips are an increasingly popular snack, but there is little understanding how cell wall polymers impact chip textures and fat contents. Raw sweetpotato slices were enzymatically treated to selectively modify cell wall polymers before frying. Chip breaking forces were lowered by protease or Viscozyme (cell wall enzyme blend) treatments, while breaking forces were increased with pectin methyl esterase. In addition, chip fat contents were reduced by the Viscozyme treatment. Since cell wall modifications could impact chip texture and fat content, cell wall polymer attributes should be considered in selection and processing of sweetpotatoes for chip manufacturing.

Sensory guided selection criteria for breeding consumer-preferred sweetpotatos in Uganda

Prioritizing sensory attributes and consumer evaluation early in breeding trials to screen for end-user preferred traits could improve adoption rates of released genotypes. In this study, a lexicon and protocol for descriptive sensory analysis (DSA) was established for sweetpotato and used to validate an instrumental texture method for which critical values for consumer preference were set. The study comprised several phases: lexicon development during a 4-day workshop; 3-day intensive panel training; follow-up virtual training, evaluation of 12 advanced genotypes and 101 additional samples from two trials in 2021 by DSA and instrumental texture analysis using TPA double compression; and DSA, instrumental texture analysis and consumer acceptability tests on 7 genotypes in on-farm trials. The established sweetpotato lexicon comprising 27 sensory attributes enabled characterization and differentiation of genotypes by sensory profiles. Significant correlation was found between sensory firmness by hand and mouth with TPA peak positive force (r = 0.695 and r = 0.648, respectively) and positive area (r = 0.748, r = 0.715, respectively). D20, NAROSPOT 1, NASPOT 8, and Umbrella were the most liked genotypes in on-farm trials (overall liking = 7). An average peak positive force of 3700 gf was proposed as a minimum texture value for screening sweetpotato genotypes, since it corresponded with at least 46 % of consumers perceiving sweetpotatoes as just-about-right in firmness and a minimum overall liking of 6 on average. Combining DSA with instrumental texture analysis facilitates efficient screening of genotypes in sweetpotato breeding programs.

Effects of a brief blanching process on quality, safety, and shelf life of refrigerated cucumber pickles

Refrigerated pickles are characterized by crisp, crunchy texture, opaque flesh, and fresh flavor. Typically produced without a thermal process, microbial safety relies on preventive controls, brine composition, and sufficient hold time prior to consumption. We hypothesized that brief blanching of whole cucumbers prior to pickling could provide an additional hurdle for pathogenic microbes without negatively impacting finished product quality. Blanch treatments (15, 90, or 180 s) in 80°C water were conducted in duplicate on two lots of cucumbers prior to cutting into spears, acidifying, and storing at 4°C. Enumeration of total aerobes, lactic acid bacteria, and glucose-fermenting coliforms was conducted for fresh and blanched cucumber. Texture, color, cured appearance development, and volatile compound profiles were analyzed for fresh and blanched cucumber and corresponding pickle products during refrigerated storage. The 90 s blanch consistently achieved a minimum 2-log reduction in cucumber microbiota and a predicted 5-log reduction of Escherichia coli O157:H7 up to 1.1 mm into the cucumber fruit. Blanching had no impact on tissue firmness during refrigerated storage for 1 year (p > 0.098). There were no differences in flavor-active lipid oxidation products (E,Z)-2,6-nonadienal and (E)-2-nonenal, and consumers (n = 110) were unable to differentiate between control and 90 s blanched cucumber pickles stored for 62 days. Exocarp color and mesocarp opacity were preserved by the blanching treatment, potentially extending product shelf life. This method offers processors an option for reducing the risk of microbial contamination while maintaining the quality attributes associated with refrigerated cucumber pickles. PRACTICAL APPLICATION: Refrigerated pickles do not undergo thermal processing, which can leave them vulnerable to microbial contamination. This study illustrates that adding a brief blanching step in refrigerated pickle processing can reduce indigenous microbiota without negatively impacting quality attributes. This blanching process could assist pickled vegetable manufacturers in providing additional safeguards for consumers while maintaining a high-quality product.

Changes in the free amino acid profile of pickling cucumber during lactic acid fermentation

Free amino acid (FAA) profiles of fresh, acidified, naturally fermented, and starter culture fermented cucumbers were analyzed by liquid chromatography triple quadrupole mass spectrometry. Fermented cucumbers contained more total FAA than acidified cucumbers (1,302 ± 102 mg/kg and 635 ± 35 mg/kg, respectively). Total FAA content of fermented cucumber was similar regardless of brine salt levels (2-6% NaCl) and starter culture addition. Glutamine (1491.4 ± 69.3 mg/kg), γ-aminobutyric acid (GABA, 269.6 ± 21.4 mg/kg), asparagine (113.0 ± 6.4 mg/kg), and citrulline (110.3 ± 8.5 mg/kg) were the most abundant FAA in fresh pickling cucumber, whereas GABA (181.3 ± 21.5 mg/kg), isoleucine (165.2 ± 11.2 mg/kg), leucine (129.8 ± 10.9 mg/kg), and lysine (110.9 ± 5.0 mg/kg) were the most abundant in fermented cucumber. GABA and ornithine were produced during fermentation, indicating glutamate decarboxylase and arginine deiminase activities. Notably, ornithine was significantly higher in natural (63.3 ± 31.5 mg/kg) versus starter culture fermented cucumbers (3.0 ± 0.7 mg/kg). This new information on FAA composition of fresh and fermented pickling cucumbers shows the impact of fermentation conditions on cucumber amino acid profiles while providing insight for manipulating fermentations for health promotion and consumer acceptance. PRACTICAL APPLICATION: This study reports changes in the free amino acid profiles of raw, fermented and acidified cucumbers, which may be valuable for understanding the impact of these foods on human health and nutrition. This information is useful for food microbiologists studying the metabolism of lactic acid bacteria during fermentation and/or designing starter cultures and could contribute to the development of novel fermented cucumber pickle products with enhanced nutritional value.

Relationships between isolated sweetpotato starch properties and textural attributes of sweetpotato French fries

Sweetpotato French fry (SPFF) textures have been associated with dry matter and starch contents, but these do not fully account for all textural differences. This study investigated the relationships between the physicochemical properties of sweetpotato starch and textural attributes of sweetpotato fries. Starches from 16 sweetpotato genotypes that varied in dry matter content were isolated and analyzed. The amylose content, pasting temperatures and viscosities, and textural properties of equilibrated starch gels were measured. Correlational analysis was performed with the respective SPFF mechanical and sensory texture attributes. Sweetpotato starch amylose content ranged from 17.3% to 21.1%, and the pasting and gel textural properties varied significantly between starches. Starch from orange-fleshed sweetpotatoes had lower pasting temperatures than starches from yellow/cream-fleshed genotypes, 72.2 ± 2.0 and 75.5 ± 1.1 °C, respectively. Notable inverse correlations were observed between the starch pasting temperature and perceived moistness (r = -0.63) and fibrousness (r = -0.70) of fries, whereas SPFF denseness was positively associated with starch pasting viscosity (r = 0.60) and nonstarch alcohol-insoluble solids content. Fry textures were likely affected by cooked starch properties, which should be considered when selecting varieties for sweetpotato fries. PRACTICAL APPLICATION: Without the aid of a batter, sweetpotato French fries (SPFFs) tend to be soft and limp-undesirable attributes in a fried food. The physiochemical properties of starch, the most abundant component in sweetpotato fries, were further explored in this study to better understand the properties of sweetpotato starch that influence SPFF textures. These findings can be used by sweetpotato processors and breeders for developing new sweetpotato varieties that are designed for production of fried products with desirable textures.

Sensory characteristics and consumer segmentation of fried sweetpotato for expanded markets in Africa

Prepared foods are increasing in popularity in West Africa alongside rapid urbanisation. Growing demand for fried products calls for targeted breeding efforts to meet consumer needs, but little is known regarding consumer preferences. This research identified the sensory attributes of fried sweetpotato preferred by different consumer groups using a combination of consumer acceptance testing and descriptive sensory analysis. Market and community surveys identified three consumer segments in Ghana and Nigeria with contrasting preferences for fried sweetpotato sensory attributes. One group preferred crispy, crunchy, mealy and sweet fried sweetpotato; another preferred characteristic yam flavour and dry texture; and the third preferred uniform orange colour appearance, ripe plantain flavour and palm nutty flavour. Such consumer segmentation can help emerging West African fried sweetpotato industries identify target markets and provides valuable information to breeders, growers and retailers to prioritise attributes in their breeding, growing or product sourcing decisions.

Development of a food product profile for boiled and steamed sweetpotato in Uganda for effective breeding

This study sought to understand user preferences of raw, boiled and steamed sweetpotato, a staple food in Uganda. A sequential methodology involving state of knowledge review, gendered food mapping, processing diagnosis and consumer testing was used in Lira and Kamwenge districts. Preferred raw sweetpotato characteristics were large roots (≥ 3 cm diameter) with a sweet taste, smooth skin and hard texture, while mealiness, sweet taste and good sweetpotato smell were important attributes for boiled sweetpotato. Processors, mostly women, highlighted ease of peeling and sappiness of raw roots. There were gender differences in quality characteristic preferences and perceived importance. The released variety, NASPOT 8, had the highest overall liking in Kamwenge and was well liked in Lira. Penalty analysis of consumer data showed that sweetness and firmness were key drivers of overall liking. The results will support breeding programmes in meeting specific end-user product profiles, selection criteria and uptake of new varieties.

Genotypic and phenotypic diversity among Lactobacillus plantarum and Lactobacillus pentosus isolated from industrial scale cucumber fermentations

The Lactobacillus plantarum and Lactobacillus pentosus genotypes existing in industrial-scale cucumber fermentations were defined using rep-PCR-(GTG)5. The ability of each genotype to ferment cucumbers under various conditions was evaluated. Rep-PCR-(GTG)5 was the technique capable of illustrating the most intraspecies discrimination compared to the sequencing of housekeeping genes (recA, dnaK, pheS and rpoA), MLST and RAPD with primers LP1, OPL5, M14 and COC. Ten genotypic clusters were defined for the 199 L. pentosus tested and three for the 17 L. plantarum clones. The ability of the 216 clones genotyped and 37 additional cucumber fermentation isolates, of the same species, to rapidly decrease the pH of cucumber juice medium under various combinations of sodium chloride (0 or 6%), initial pH (4.0 or 5.2) and temperatures (15 or 30 °C) was determined using a fractional factorial screening design. A reduced fermentation ability was observed for the L. plantarum strains as compared to L. pentosus, except for clone 3.2.8, which had a ropy phenotype and aligned to genotypic cluster A. L. pentosus strains belonging to three genotypic clusters (B, D and J) were more efficient in cucumber juice fermentation as compared to most L. plantarum strains. This research identified three genetically diverse L. pentosus strains and one L. plantarum as candidates for starter cultures for commercial cucumber fermentations.

Modeling buffer capacity and pH in acid and acidified foods

Standard ionic equilibria equations may be used for calculating pH of weak acid and base solutions. These calculations are difficult or impossible to solve analytically for foods that include many unknown buffering components, making pH prediction in these systems impractical. We combined buffer capacity (BC) models with a pH prediction algorithm to allow pH prediction in complex food matrices from BC data. Numerical models were developed using Matlab software to estimate the pH and buffering components for mixtures of weak acid and base solutions. The pH model was validated with laboratory solutions of acetic or citric acids with ammonia, in combinations with varying salts using Latin hypercube designs. Linear regressions of observed versus predicted pH values based on the concentration and pK values of the solution components resulted in estimated slopes between 0.96 and 1.01 with and without added salts. BC models were generated from titration curves for 0.6 M acetic acid or 12.4 mM citric acid resulting in acid concentration and pK estimates. Predicted pH values from these estimates were within 0.11 pH units of the measured pH. Acetic acid concentration measurements based on the model were within 6% accuracy compared to high-performance liquid chromatography measurements for concentrations less than 400 mM, although they were underestimated above that. The models may have application for use in determining the BC of food ingredients with unknown buffering components. Predicting pH changes for food ingredients using these models may be useful for regulatory purposes with acid or acidified foods and for product development. PRACTICAL APPLICATION: Buffer capacity models may benefit regulatory agencies and manufacturers of acid and acidified foods to determine pH stability (below pH 4.6) and how low-acid food ingredients may affect the safety of these foods. Predicting pH for solutions with known or unknown buffering components was based on titration data and models that use only monoprotic weak acids and bases. These models may be useful for product development and food safety by estimating pH and buffering capacity.

Comparative genomics of eight Lactobacillus buchneri strains isolated from food spoilage

Abstract

Background

Lactobacillus buchneri is a lactic acid bacterium frequently associated with food bioprocessing and fermentation and has been found to be either beneficial or detrimental to industrial food processes depending on the application. The ability to metabolize lactic acid into acetic acid and 1,2-propandiol makes L. buchneri invaluable to the ensiling process, however, this metabolic activity leads to spoilage in other applications, and is especially damaging to the cucumber fermentation industry. This study aims to augment our genomic understanding of L. buchneri in order to make better use of the species in a wide range of applicable industrial settings.

Results

Whole-genome sequencing (WGS) was performed on seven phenotypically diverse strains isolated from spoiled, fermented cucumber and the ATCC type strain for L. buchneri, ATCC 4005. Here, we present our findings from the comparison of eight newly-sequenced and assembled genomes against two publicly available closed reference genomes, L. buchneri CD034 and NRRL B-30929. Overall, we see ~ 50% of all coding sequences are conserved across these ten strains. When these coding sequences are clustered by functional description, the strains appear to be enriched in mobile genetic elements, namely transposons. All isolates harbor at least one CRISPR-Cas system, and many contain putative prophage regions, some of which are targeted by the host’s own DNA-encoded spacer sequences.

Conclusions

Our findings provide new insights into the genomics of L. buchneri through whole genome sequencing and subsequent characterization of genomic features, building a platform for future studies and identifying elements for potential strain manipulation or engineering.

Effect of Brine Acidification on Fermentation Microbiota, Chemistry, and Texture Quality of Cucumbers Fermented in Calcium or Sodium Chloride Brines

Commercial fermentation for bulk preservation of cucumbers relies on natural microbiota and approximately 1 M sodium chloride (NaCl) brines, resulting in large volumes of high-salt wastewater. An alternative process utilizing 0.1 M calcium chloride (CaCl₂ ) as the only salt was developed to eliminate NaCl from fermentation brines for reduced environmental impact. This study determined the effect of brine acidification on the fermentation microbiota and texture quality of cucumbers fermented in CaCl₂ brines. Cucumber fermentations were conducted in sealed glass jars for six independent lots of cucumbers in a randomized complete block design with a full-factorial treatment structure for brine acidification (acetic acid, hydrochloric acid, or nonacidified) and brining salt (1 M NaCl or 0.1 M CaCl₂ ). Enterobacteriaceae spp. survived longer and were >1 log colony forming units/mL higher in fermenting cucumbers than in brines. Addition of 25 mM acetic acid to fermentation brines (but not the addition of hydrochloric acid at the same pH) reduced Enterobacteriaceae spp. in brines and cucumbers (P < 0.002) during the initiation of fermentation for both brining salts. However, acidification had no effect on texture quality of fermented cucumbers (P = 0.8235). Despite differences in early fermentation microbiota, fermentation of cucumbers in calcium chloride brines under controlled conditions, with or without acidification, resulted in high retention of tissue firmness. These results differ from fermentations in a commercial setting initiated in brines of neutral pH, indicating that production variables, such as air exposure, interact with brining in CaCl₂ to negatively affect the texture quality of fermented cucumbers. PRACTICAL APPLICATION: This study examined the effects of initial brine acidification on the course of lactic acid fermentation and resulting texture quality of cucumbers fermented in calcium or sodium salt brines. Fermentation brines containing acetic acid (the acid in vinegar) reduced the pH of the cucumber and the soil-associated Enterobacteriaceae spp. most rapidly, and favored the conversion of sugars to lactic acid. Interestingly, the texture quality was not affected by brine acidification, and all cucumbers fermented in calcium brines in the absence of air retained their firmness during fermentation and bulk storage.

Metabolite Profiles of Raw Peanut Seeds Reveal Differences between Market-Types

Peanuts (Arachis hypogaea L.) are prized for their flavor and popular worldwide as food or as food ingredients. The raw peanut seed contains the precursor compounds to roasted peanut flavor and has the potential to be manipulated through traditional breeding methods. However, little is known about the metabolome of the raw seeds. Comprehensive metabolite profiles of both raw runner and Virginia-type peanuts were determined. Using a system incorporating several methodologies including (RP)/UPLC-MS/MS and HILIC/UPLC-MS/MS, along with quantitation of fatty acids, free amino acids, and tocopherols, 365 metabolites were identified and of these, 52 were significantly different between market types (P < 0.05). Higher levels of gamma-glutamylalanine, oxylipins, purine metabolites, and alpha-ketoglutarate derived members of the glutamate family of amino acids defined the Virginia-type, while runner-type peanuts were differentiated by their ethylmalonate and eicosenoate content. This study presents a comprehensive analysis of the raw peanut seed, providing knowledge of the range of small molecules present in peanuts. The new information presented here will enable future research for peanut quality improvement. PRACTICAL APPLICATION: Peanuts are widely used as snack foods and as food ingredients. Knowledge of the secondary metabolite compounds in raw peanuts is needed to determine their importance in peanut flavor and nutritional quality. This report used a nontargeted analytical approach for the identification of these types of compounds in peanuts for the first time. These data were supplemented with quantitative analysis of free amino acids and tocopherols and discussed as potential flavor precursors and health promoting compounds.

Discovery and quantification of bioactive peptides in fermented cucumber by direct analysis IR-MALDESI mass spectrometry and LC-QQQ-MS

Bioactive peptides have been identified in lactic acid bacteria fermented foods including cultured milk, sourdough, and cured meats; however, their presence has not been investigated in fermented vegetables. In this study, infrared, matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry (MS) was employed to identify bioactive peptides in fermented cucumber. Natural and starter culture fermented cucumbers were prepared in triplicate in sodium chloride brines and compared to acidified cucumbers. Putative matches of known food-derived bioactive peptides were identified by direct analysis using IR-MALDESI-MS. Peptides were confirmed by IR-MALDESI MS/MS and quantified by LC-MS/MS. Three angiotensin converting enzyme (ACE) inhibitory peptides, IPP (0.42-0.49 mg/kg), LPP (0.30-0.33 mg/kg), and VPP (0.32-0.35 mg/kg) were formed in fermented cucumbers. A fourth ACE inhibitory peptide, KP (0.93-1.5 mg/kg), was enhanced 3-5 fold in fermented cucumbers compared with acidified cucumbers. This work demonstrates that lactic acid bacteria fermentation can enhance bioactive peptide content in vegetables.

Chemical Constituents of Sweetpotato Genotypes in Relation to Textural Characteristics of Processed French Fries

Sweetpotato French fries (SPFF) are growing in popularity, however limited information is available on SPFF textural properties in relation to chemical composition. This study investigated the relationship between chemical components of different sweetpotato varieties and textural characteristics of SPFF. Sixteen sweetpotato genotypes were evaluated for (1) chemical constituents; (2) instrumental and sensory textural properties of SPFF; and (3) the relationship between chemical components, instrumental measurements, and sensory attributes. Dry matter (DM), alcohol-insoluble solids (AIS), starch, sugar, and oil content, and also α- and β-amylase activities were quantified in raw sweetpotatoes and SPFF. Peak force and overall hardness describing instrumental textural properties of SPFF were measured using a texture analyzer. Descriptive sensory analysis was conducted and 10 attributes were evaluated by a trained panel. Results showed that DM, AIS, and starch content in raw sweetpotatoes were significantly correlated (P < 0.05) with instrumental peak force and overall hardness (r = 0.41 to 0.68), and with sensory surface roughness, hardness, fracturability, and crispness (r = 0.63 to 0.90). Total sugar content in raw sweetpotatoes was positively correlated with sensory smoothness and moistness (r = 0.77), and negatively correlated with instrumental peak force and overall hardness (r = -0.62 to -0.69). Instrumental measurements were positively correlated with sensory attributes of hardness, fracturability, and crispness (r = 0.68 to 0.96) and negatively correlated with oiliness, smoothness, moistness, and cohesiveness (r = -0.61 to -0.91). Therefore, DM, AIS, starch, and total sugar contents and instrumental measurements could be used as indicators to evaluate sweetpotato genotypes for SPFF processing.

PRACTICAL APPLICATION

In recent years, sweetpotato French fries (SPFF) have grown in popularity, but limited information is available on SPFF textural properties in relation to the differences in chemical constituents among sweetpotato varieties. This study demonstrated that sensory texture attributes of SPFF varied widely and were significantly correlated with chemical components such as dry matter, starch, and total sugar contents of raw sweetpotatoes and instrumental texture measurements of SPFF. The knowledge generated from this study will benefit the food industry and breeding programs with the selection of sweetpotato varieties for improved SPFF quality.

Direct Analysis of Triterpenes from High-Salt Fermented Cucumbers Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization (IR-MALDESI)

High-salt samples present a challenge to mass spectrometry (MS) analysis, particularly when electrospray ionization (ESI) is used, requiring extensive sample preparation steps such as desalting, extraction, and purification. In this study, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) coupled to a Q Exactive Plus mass spectrometer was used to directly analyze 50-μm thick slices of cucumber fermented and stored in 1 M sodium chloride brine. From the several hundred unique substances observed, three triterpenoid lipids produced by cucumbers, β-sitosterol, stigmasterol, and lupeol, were putatively identified based on exact mass and selected for structural analysis. The spatial distribution of the lipids were imaged, and the putative assignments were confirmed by tandem mass spectrometry performed directly on the same cucumber, demonstrating the capacity of the technique to deliver confident identifications from highly complex samples in molar concentrations of salt without the need for sample preparation. Graphical Abstract ᅟ.

Development and Validation of a Near-Infrared Spectroscopy Method for the Prediction of Acrylamide Content in French-Fried Potato

This study investigated the ability of near-infrared spectroscopy (NIRS) to predict acrylamide content in French-fried potato. Potato flour spiked with acrylamide (50-8000 μg/kg) was used to determine if acrylamide could be accurately predicted in a potato matrix. French fries produced with various pretreatments and cook times (n = 84) and obtained from quick-service restaurants (n = 64) were used for model development and validation. Acrylamide was quantified using gas chromatography-mass spectrometry, and reflectance spectra (400-2500 nm) of each freeze-dried sample were captured on a Foss XDS Rapid Content Analyzer-NIR spectrometer. Partial least-squares (PLS) discriminant analysis and PLS regression modeling demonstrated that NIRS could accurately detect acrylamide content as low as 50 μg/kg in the model potato matrix. Prediction errors of 135 μg/kg (R(2) = 0.98) and 255 μg/kg (R(2) = 0.93) were achieved with the best PLS models for acrylamide prediction in Russet Norkotah French-fried potato and multiple samples of unknown varieties, respectively. The findings indicate that NIRS can be used as a screening tool in potato breeding and potato processing research to reduce acrylamide in the food supply.

Characterization of cucumber fermentation spoilage bacteria by enrichment culture and 16S rDNA cloning

Commercial cucumber fermentations are typically carried out in 40000 L fermentation tanks. A secondary fermentation can occur after sugars are consumed that results in the formation of acetic, propionic, and butyric acids, concomitantly with the loss of lactic acid and an increase in pH. Spoilage fermentations can result in significant economic loss for industrial producers. The microbiota that result in spoilage remain incompletely defined. Previous studies have implicated yeasts, lactic acid bacteria, enterobacteriaceae, and Clostridia as having a role in spoilage fermentations. We report that Propionibacterium and Pectinatus isolates from cucumber fermentation spoilage converted lactic acid to propionic acid, increasing pH. The analysis of 16S rDNA cloning libraries confirmed and expanded the knowledge gained from previous studies using classical microbiological methods. Our data show that Gram-negative anaerobic bacteria supersede Gram-positive Fermincutes species after the pH rises from around 3.2 to pH 5, and propionic and butyric acids are produced. Characterization of the spoilage microbiota is an important first step in efforts to prevent cucumber fermentation spoilage.

PRACTICAL APPLICATION

An understanding of the microorganisms that cause commercial cucumber fermentation spoilage may aid in developing methods to prevent the spoilage from occurring.

Characteristics of spoilage-associated secondary cucumber fermentation

Secondary fermentations during the bulk storage of fermented cucumbers can result in spoilage that causes a total loss of the fermented product, at an estimated cost of $6,000 to $15,000 per affected tank. Previous research has suggested that such fermentations are the result of microbiological utilization of lactic acid and the formation of acetic, butyric, and propionic acids. The objectives of this study were to characterize the chemical and environmental conditions associated with secondary cucumber fermentations and to isolate and characterize potential causative microorganisms. Both commercial spoilage samples and laboratory-reproduced secondary fermentations were evaluated. Potential causative agents were isolated based on morphological characteristics. Two yeasts, Pichia manshurica and Issatchenkia occidentalis, were identified and detected most commonly concomitantly with lactic acid utilization. In the presence of oxygen, yeast metabolic activities lead to lactic acid degradation, a small decline in the redox potential (E(h), Ag/AgCl, 3 M KCl) of the fermentation brines, and an increase in pH to levels at which bacteria other than the lactic acid bacteria responsible for the primary fermentation can grow and produce acetic, butyric, and propionic acids. Inhibition of these yeasts by allyl isothiocyanate (AITC) resulted in stabilization of the fermented medium, while the absence of the preservative resulted in the disappearance of lactic and acetic acids in a model system. Additionally, three Gram-positive bacteria, Lactobacillus buchneri, a Clostridium sp., and Pediococcus ethanolidurans, were identified as potentially relevant to different stages of the secondary fermentation. The unique opportunity to study commercial spoilage samples generated a better understanding of the microbiota and environmental conditions associated with secondary cucumber fermentations.

A chemical basis for sour taste perception of acid solutions and fresh-pack dill pickles

Sour taste is influenced by pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity in foods containing organic acids. The objective of this study was to investigate the roles of protonated (undissociated) organic acid species and hydrogen ions in evoking sour taste. Sour taste intensity increased linearly with hydrogen ion concentration (R(2)= 0.995), and with the concentration of protonated organic acid species at pH 3.5 (R(2)= 0.884), 4.0 (R(2)= 0.929), and 4.5 (R(2)= 0.975). The structures of organic acid molecules did not affect sour taste after adjusting for the effects of protonated organic acid species and hydrogen ions. Sour taste intensity was also linearly related to the total concentration of protonated organic acid species in fresh-pack dill pickles (R(2)= 0.957). This study showed that the sour taste of organic acids was directly related to the number of molecules with at least 1 protonated carboxyl group plus the hydrogen ions in solution. Conclusions from these results are that all protonated organic acids are equally sour on a molar basis, that all protonated species of a given organic acid are equally sour, and that hydrogen ions and protonated organic acids are approximately equal in sour taste on a molar basis. This study provides a new understanding of the chemical species that are able to elicit sour taste and reveals a basis for predicting sour taste intensity in the formulation of acidified foods.

The chemistry and physiology of sour taste--a review

Sour taste is the key element in the flavor profile of food acidulants. Understanding the chemistry and physiology of sour taste is critical for efficient control of flavor in the formulation of acid and acidified foods. After a brief introduction to the main applications of food acidulants, several chemical parameters associated with sour taste are discussed. Special emphasis is given to hydrogen ions, protonated (undissociated) acid species, titratable acidity, anions, molar concentration, and physical and chemical properties of organic acids. This article also presents an overview of the physiology of sour taste and proposed theories for the transduction mechanisms for sour taste. The physiology of sour taste perception remains controversial and significant diversity exists among species with regard to cellular schemes used for detection of stimuli. The variety of mechanisms proposed, even within individual species, highlights the complexity of elucidating sour taste transduction. However, recent evidence suggests that at least one specific sour taste receptor protein has been identified.