Effect of ripening and variety on the physiochemical quality and flavor of fermented Chinese chili pepper (Paojiao)

An efficient method for chili pepper variety classification and origin tracing based on an electronic nose and deep learning

The quality of chili peppers is closely related to their variety and geographical origin. The market often substitutes high-quality chili peppers with inferior ones, and cross-contamination occurs during processing. The existing methods cannot quickly and conveniently distinguish between different chili varieties or origins, which require expensive experimental equipment and professional skills. Techniques such as energy-dispersive X-ray fluorescence and inductively coupled plasma spectroscopy have been used for chili pepper classification and origin tracing, but these methods are either costly or destructive. To address the challenges of accurately identifying chili pepper varieties and origin tracing of chili peppers, this paper presents a sensor-aware convolutional network (SACNet) integrated with an electronic nose (e-nose) for accurate variety classification and origin traceability of chili peppers. The e-nose system collects gas samples from various chili peppers. We introduce a sensor attention module that adaptively focuses on the importance of each sensor in gathering gas information. Additionally, we introduce a local sensing and wide-area sensing structure to specifically capture gas information features, enabling high-precision identification of chili pepper gases. In comparative experiments with other networks, SACNet demonstrated excellent performance in both variety classification and origin traceability, and it showed significant advantages in terms of parameter quantity. Specifically, SACNet achieved 98.56 % accuracy in variety classification with Dataset A, 97.43 % accuracy in origin traceability with Dataset B, and 99.31 % accuracy with Dataset C. In summary, the combination of SACNet and an e-nose provides an effective strategy for identifying the varieties and origins of chili peppers.

Characterization of Thirty Germplasms of Millet Pepper (Capsicum frutescens L.) in Terms of Fruit Morphology, Capsaicinoids, and Nutritional Components

BACKGROUND

Millet peppers have rich and diverse germplasm resources. It is of great significance to characterize their phenotypes and physicochemical indicators.

METHODS

30 millet germplasms were selected to measure the fruit length and width, flesh thickness, number of ventricles, fruit stalk length, and single fruit weight, and the texture characteristics of fruit such as hardness, cohesiveness, springiness, gumminess, and chewiness were determined by a texture analyzer. At the same time, high-performance liquid chromatography (HPLC) and gas chromatography (GC) were used to determine the fruit of capsaicin, dihydrocapsaicin, nordihydrocapsaicin, fatty acids, vitamin E (VE), total phenol, total sugar, and total dietary fiber.

RESULTS

M11 showed outstanding parameters in phenotype and texture. The coefficient of variation (CV) for VE was as high as 94.943% and the highest diversity index (H') was total soluble solid, at 1.988%. M5 and M18 contained rich and diverse fatty acids. At the same time, the content of capsaicinoids in M18 also ranks among the top, second only to M27 (with a total capsaicin content of 5623.96 μg/g). PCA analysis using phenotypic data and physicochemical data showed that the classification results were different. Further hierarchical group analysis was carried out using all the index data. The results showed that 30 millet pepper germplasms were divided into three new categories: M5, M9, M18, and M24 formed one group (C1), M10, M14, M16, M19, M20, M22, M25, M26, M28, M29, and M30 formed another cluster (C2), and the remaining germplasms formed a third cluster (C3). Among them, the abundance of fatty acids in the C1 germplasm was higher than that in the other two groups.

CONCLUSIONS

Our study showed that different germplasms had significant differences in morphological traits and nutritional metabolic components and were rich in genetic diversity. This study provides a theoretical basis for the improvement of millet varieties and the development of functional food.

Analysis on microbial communities and characteristic flavor metabolic of PXDB-meju by partially substituting wheat flour with soybean flour and gluten flour

Pixian Douban (PXDB) is one of the most popular condiments in China due to its unique flavor. Wheat flour that contains abundant nutrients is an important raw material in producing flavors during PXDB fermentation. In this study, wheat flour was substituted with soybean flour and gluten flour that have higher proteins in portions of 10.4% and 4.2% (F1), 8.9% and 7.2% (F2), 9.6% and 5.8% (F3). The results indicated that the substitutions increased the amino acid nitrogen content and improved flavor quality compared with traditional group (CT). Especially, the key amino acids including spartate, glutamic, arginine and lysine, and the phenylacetaldehyde as one of the most important volatile compounds exhibited preferable higher contents in F2 group than those in CT group. Metagenomic analysis showed that the abundances of predominant bacteria, including Kosakonia_cowanii, unclassified_f__Enterobacteriaceae and unclassified_g__Enterobacter, were higher in the F2 compared to the CT. Lupinus_albus and Plutella_xylostella were the top two fungi in relative abundance, with higher growth rates in F2 than in CT. Furthermore, metabolism pathway analysis revealed higher relative abundance of enzymes producing key amino acids and phenethylaldehyde in the F2 compared to the CT. Meanwhile, these enzymes were exclusively annotated to the Kosakonia_cowanii, Bacillus_velezensis and Escherichia_coli in F2. This study provided a theoretical foundation for improving PXDB flavor quality in industry production.

Effect of magnetic field treatment on the softening of green chilies (Capsicum annuum L.) during storage

In this study, effects of magnetic field treatment on the softening of green chilies during storage (0-30 d at 10 °C) were investigated, and the cell wall polysaccharide content, modifying enzyme activities, water distribution, and cell wall structure were determined. After 30 d of storage, the weight loss of the green chilies in conventional refrigeration (CR) group reached 35.40 %, whereas it was 20.96 % and 29.85 % in the static (SMF; 4 mT) and alternating magnetic field (AMF; 4 mT, 1 Hz) groups, respectively. Furthermore, magnetic field treatment maintained low levels of water-soluble pectin (WSP) and high levels of chelate-soluble pectin (CSP) and sodium carbonate-soluble pectin (NSP) in the green chilies. The degree of methylation (DE) values of WSP and NSP in the pre-treated samples were 0.37 and 0.18, respectively. Conversely, at the end of storage, the DE values of WSP and NSP in the CR, SMF, and AMF groups decreased to 0.12 and 0.05, 0.25 and 0.11, and 0.18 and 0.07, respectively, suggesting that magnetic field treatment had a negative influence on the demethylation of pectin. Magnetic field treatment also decreased the activities of pectin methyl esterase, polygalacturonase, and β-galactosidase in the green chilies, maintaining them at a low level. The magnetic field treatment resulted in a higher free water content in green chilies compared to the CR, exceeding the CR group's content by 1.79 % and reaching 88.18 % at the terminal storage. Scanning electron microscopy results revealed that magnetic field treatment maintained the structural integrity of the cell wall in the green chilies. The results of this study confirmed the applicability of magnetic field treatment in maintaining the firmness and reducing the weight loss of the green chilies, thus prolonging their shelf life.

Characterization of key aroma-active compounds in fermented chili pepper (Capsicum frutescens L.) using instrumental and sensory techniques

The aroma profile of fermented chili pepper was analyzed using gas chromatography-mass spectrometry (GC-MS) coupled with chromatography-olfactometry (GC-O). A total of 19 aroma-active compounds were detected, exhibiting aroma intensities spanning from 1.8 to 4.2. And 12 aroma-active compounds were determined as pivotal odorants through odor activity value (OAV) calculation. Concentrations of these aroma-active compounds were quantified and subsequently employed in reconstructing the aroma profile of fermented chili pepper. Quantitative descriptive sensory analysis and electronic nose analysis proved that the aroma profile of fermented chili pepper was basically reconstituted. Omission experiments confirmed that methyl salicylate, linalool, 2-methoxy-3-isobutylpyrazine, and phenylethyl alcohol were the key aroma-active compounds of fermented chili pepper. Moreover, the perceptual interactions between the key aroma-active compounds were investigated. It was found that methyl salicylate masked the floral aroma, while phenylethyl alcohol had an additive effect on the aroma of linalool and 2-methoxy-3-isobutylpyrazine.

Effect of salt concentration on the quality and microbial community during pickled peppers fermentation

This work aimed to investigate the effect of salt concentration on the quality and microbial community of pickled peppers during fermentation, and the cross-correlation between microorganisms and quality was also revealed. The results showed that 9 volatile flavor compounds were unique to the low salt concentration group (D group), which also contained higher content of FAA, lactic acid and acetic acid than high salt concentration group (G group). Meanwhile, the samples of D2 group have a better texture properties. Firmicutes, Proteobacteria, Ascomycota, Lactobacillus, Pectobacterium, and Pseudomonas were detected as the main microbial community during the fermentation with different salt concentrations. Furthermore, the correlations analysis results indicated that the salt concentration has a significant effect on the microbial community of pickled peppers (p < 0.001), and Pediococcus, Lactobacillus, Cedecca, Issatchenkia, Pichia, Kazachstania, and Hanseniaspora were significantly correlated with flavors, which played crucial roles in the unique flavor formation of pickled peppers.

Effect of adding various supplements on physicochemical properties and starch digestibility of cooked rice

This study investigated the physicochemical modifications of cooked rice caused by adding various supplements (rapeseed oil, dried wasabi powder, and dried chili pepper powder). The physicochemical and digestive properties of treated cooked rice were analyzed using multiple techniques to determine the impact of supplements on the rice quality, including its starch digestibility. All samples with added supplements showed an increase in surface firmness (0.77-0.95 kg·m/s2 (N)) and a decrease in thickness (2.23-2.35 mm) and surface adhesiveness (1.43-7.22 J/m3). Compared to the control group, two absorption peaks at 2856 and 1748 cm-1 and new signals at 1683 and 1435 cm-1 appeared in the Fourier transform infrared (FTIR) spectroscopy. Analysis of FTIR results revealed that the interaction force was mainly through noncovalent interactions. Moreover, adding supplements increased the resistant starch (RS) levels in all samples. Scanning electron microscopy (SEM) suggested that oil-enriched phases, proteins, and polyphenols could cause large agglomeration and loose gel structure. These results suggested the formation of amylose-guest molecule complexes, which may influence starch functionality. Our work could provide insight into the starch-supplement interactions and the key factors affecting starch digestibility.

Varietal influence on bioactive compounds and antioxidant activity in chilies during development stages

Numerous cultivars of chili are grown in Bangladesh for their nutritional and sensory attributes, serving as both spices and food items. Among many, indigenous chili cultivars in Bangladesh include Sada Akshi, Kajini, Dhani, and Naga are the important ones. The functional qualities of chili peppers are attributed to the plentiful presence of bioactive substances. Consequently, this study aimed to determine the variations in bioactive compounds, antioxidant activities, and hotness among the pre-mature, mature, pre-ripening, and ripening stages of four distinct chili cultivars. Four different cultivars of chilis at four different maturity stages were collected and analyzed for their antioxidant and bioactive profiles. The findings of the research revealed that all chili varieties exhibited a notable range of vitamin C concentration, ranging from 1.67 to 8.45 mg/g FW during the maturity stages. The values of TPC, TFC, total carotenoids, and chlorophyll a and b ranged from 16.68 to 46.76 mg GAE/g, 2.80-8.53 mg QE/g, 4.31-85.79 μg/g DW, 2.83-15.54 and 0.74-5.66 μg/g DW on a dry weight basis, respectively. The antioxidant activity was assessed using the FRAP and the DPPH scavenging assay and the values ranged from 142.62 to 311.03 mM Fe (II) Equivalent/100g DW and 216.36-329.52 μM Trolox Equivalent/g DW, respectively. The content of vitamin C, TPC, total carotenoids, and chlorophyll b was increased with the stages of development. The hotness of chili also increased with the development stages. However, the antioxidant activity fluctuated during the development stages of chili. Furthermore, the study incorporated the evaluation of physical parameters, such as height, weight, and color attributes concerning chilies. The Naga variety of chili demonstrated the highest level of efficacy when compared to other varieties. The nutritional and physicochemical information of the different cultivars of chili in this study might be useful to the breeders, spice processors, and consumers for desired size, taste, and hotness with health-promoting bioactive compounds, eventually for determining the harvest time.

Revealing core functional microorganisms in the fermentation process of Qicaipaojiao (Capsicum annuum L.) based on microbial metabolic network

Paojiao, a typical Chinese traditional fermented pepper, is favored by consumers for its unique flavor profile. Microorganisms, organic acids, amino acids, and volatile compounds are the primary constituents influencing the development of paojiao's flavor. To elucidate the key flavor compounds and core microorganisms of Qicaipaojiao (QCJ), this study conducted a comprehensive analysis of the changes in taste substances (organic acids and amino acids) and volatile flavor compounds during QCJ fermentation. Key flavor substances in QCJ were identified using threshold aroma value and odor activity value and the core microorganisms of QCJ were determined based on the correlation between dominant microorganisms and the key flavor substances. During QCJ fermentation, 16 key taste substances (12 free amino acids and 4 organic acids) and 12 key aroma substances were identified. The fermentation process involved 10 bacteria and 7 fungal genera, including Lactiplantibacillus, Leuconostoc, Klebsiella, Pichia, Wickerhamomyces, and Candida. Correlation analysis revealed that the core functional microorganisms encompassed representatives from 8 genera, including 5 bacterial genera (Lactiplantibacillus, Weissella, Leuconostoc, Klebsiella, and Kluyvera) and 3 fungal genera (Rhodotorula, Phallus, and Pichia). These core functional microorganisms exhibited significant correlations with approximately 70 % of the key flavor substances (P < 0.05). This study contributes to an enhanced understanding of flavor formation mechanisms and offers valuable insight into flavor quality control in food fermentation processes.

The role of water distribution, cell wall polysaccharides, and microstructure on radish (Raphanus sativus L.) textural properties during dry-salting process

Radish (Raphanus sativus L.) undergoes texture changes in their phy-chemical properties during the long-term dry-salting process. In our study, we found that during the 60-day salting period, the hardness and crispness of radish decreased significantly. In further investigation, we observed that the collaborative action of pectin methylesterase (PME) and polygalacturonase (PG) significantly decreased the total pectin, alkali-soluble pectin (ASP), and chelator-soluble pectin (CSP) content, while increasing the water-soluble pectin (WSP) content. Furthermore, the elevated activities of cellulase and hemicellulase directly led to the notable fragmentation of cellulose and hemicellulose. The above reactions jointly induced the depolymerization and degradation of cell wall polysaccharides, resulting in an enlargement of intercellular spaces and shrinkage of the cell wall, which ultimately led to a reduction in the hardness and crispness of the salted radish. This study provided key insights and guidance for better maintaining textural properties during the dry-salting process of radish.

Effects of substrates and suppliers of ingredients on microbial community and metabolites of traditional non-salt Suancai

Aim: Non-salt Suancai is an acidic fermented vegetable consumed by the Chinese Yi ethnic group. Traditionally, it is produced by fermentation without salt in a cold environment. The present study aimed to investigate the metabolite and microbial characteristics, and the effects of substrates/suppliers ingredients on non-salt Suancai. Methods: A simulated fermentation system of non-salt Suancai was constructed by using different substrates/suppliers' ingredients. The coherence and differential detection of the metabolite and microbial characteristics were done through non-target metabolomic and metagenomic analysis. Results: Lactic acid was the predominant organic acid across all samples. The enumeration of the Lactic acid bacteria showed no discernible differences between study groups, but that of yeast was highest in the mustard leaf stem (Brassica juncea var. latipa). The three major biological metabolic pathways were metabolism, environmental information, and genetic information processing based on the KEGG database. The metabolite diversity varied with the substrate/supplier of ingredients based on the PLS-DA plot. Lactiplantibacillus, Leuconostoc, and Lactococcus were prevalent in all samples but differentially. The microbial diversity and richness varied significantly, with 36~291 species being identified. Among the various substrates collected from the same supplier, 29, 59, and 29 differential species were identified based on LEfSe [linear discriminant analysis (LDA) > 2, P < 0.05]. Leuconostoc citreum, Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, Lactiplantibacillus plantarum, and Leuconostoc lactis were likely to be used as the species to discriminate samples collected from different suppliers. Conclusions: This research contributed to the exploration of microbial and metabolite characteristics behind the ingredient restriction of non-salt Suancai using traditional technology.

The Health-Promoting Quality Attributes, Polyphenols, Iridoids and Antioxidant Activity during the Development and Ripening of Cornelian Cherry (Cornus mas L.)

This study defined the physicochemical attributes, composition, and antioxidant capacity of four Polish cultivars of cornelian cherry (CC) at six stages of development and ripening. A total of 52 metabolites were identified by UPLC-ESI-qTOF-MS/MS and quantified by HPLC-PDA. In general, phenolic acids, hydrolyzable tannins, flavonols, iridoids, antioxidant activity, organic acids, and vitamin C decreased, while anthocyanins, malic acid, sugars, and titratable acidity increased. For the first time, we determined the evolution of the CC chemical properties and the metabolic behavior and quantified the individual compounds, and groups of compounds during ripening, in particular gallotannins, ellagitannins, iridoids, and organic acids. The main novelty of our study is that CC is a valuable resource for utilization at different degrees of maturity. We showed that unripe fruits in particular deserve valorization, as they contained the highest content of total bioactive phytocompounds (5589.1-6779.6 mg/100 g dw)-primarily phenolic acids > iridoids > tannins-and the highest antioxidant capacity. The intermediate stages were the most abundant in vitamin C (341.1-495.6 mg/100 g dw), ellagic acid (5.9-31.6 mg/100 g dw), gallotannins (47.8-331.1 mg/100 g dw), and loganic acid (1393.0-2839.4 mg/100 g dw). The ripe fruits contained less bioactive phytocompounds (1403.7-1974.6 mg/100 g dw)-primarily iridoids > phenolic acids > tannins > anthocyanins-and the lowest antioxidant capacity. On the other hand, ripe fruits showed the highest content of anthocyanins (30.8-143.2 mg/100 g dw), sugars (36.4-78.9 g/100 g dw), malic acid (5.5-12.2 g/100 g dw), and, favorably for the nutritional applications, the highest sugar-to-acids ratio (3.0-6.4). Our work illustrates in detail that quality attributes and the content of health-promoting phytocompounds in CC depend on the ripening stage and on the cultivar. These results advance the scientific knowledge about CC. Our findings can be helpful to select the optimal properties of CC for the development of diverse functional foods and phytopharmaceuticals applied in the prevention of civilization diseases.

Effect of pasteurization processing and storage conditions on softening of acidified chili pepper: Pectin and it related enzymes

The softening of acidified chili peppers induced by processing and storage has become a major challenge for the food industry. This study aims to explore the impact of pasteurization techniques, thermal processing (TP), high-pressure processing (HPP), addition of sodium metabisulfite (SMS), and storage conditions (25 °C, 37 °C, and 42 °C for 30 days) on the texture-related properties of acidified chili pepper. The results showed that the textural properties of samples were destructed by TP (the hardness of samples decreased by 19.43 %) but were less affected by HPP and SMS. Compared with processing, storage temperature had a more dominant impact on texture and pectin characteristics. With increased storage temperature, water-solubilized pectin fraction content increased (increased by 160.99 %, 136.74 %, and 13.01 % in TP, HPP, and SMS-stored groups, respectively), but sodium carbonate-solubilized pectin fraction content decreased (decreased by 29.84 %, 26.81 %, and 8.60 % in TP-, HPP-, and SMS-stored groups, respectively), especially in TP-stored groups. Multivariate data analysis showed that softening was more closely related to pectin conversion induced by acid hydrolysis and pectinase depolymerization. This finding offers new perspectives for the production of acidified chili pepper.

Effect of raw material frozen storage on physicochemical properties and flavor compounds of fermented mandarin fish (Siniperca chuatsi)

Frozen mandarin fish (MF) is utilized for preparation fermented MF. However, how raw material (RM) affects the quality and flavor of fermented MF is unclear. This study investigated the impact and mechanism of RM frozen storage on the microstructure, texture, water distribution, and flavor of fermented MF by light microscopy, texture profile analysis, low-field nuclear magnetic resonance, gas chromatography-ion mobility spectrometry, and multivariate analysis. With increasing RM frozen storage time, both frozen MF and frozen-based fermented MF decreased in muscle fiber density while increased in muscle fiber diameter. Additionally, RM frozen storage exhibited a significant impact on the water distribution of frozen MF, while no obvious effect on that of frozen-based fermented MF. Seven odorant (2-methyl-1-propanol, 3-hydroxy-2-butanone, 2,3-butanedione, hexanal-D, ethyl acetate-D, 3-pentanone, and acetone) were shown as potential markers to distinguish fermented MF. This study could provide a theoretical basis for the production of high-quality frozen-based fermented MF.

Effect of Capsaicin Stress on Aroma-Producing Properties of Lactobacillus plantarum CL-01 Based on E-Nose and GC-IMS

Capsaicin stress, along with salt stress, could be considered the main stressors for lactic acid bacteria in traditional fermented pepper products. Until now, insufficient attention has been paid to salt stress, while the effect of capsaicin on the aroma-producing properties of Lactobacillus plantarum (L. plantarum) is unclear. The present study attempted to illustrate the effect of capsaicin stress on the aroma-producing properties of L. plantarum CL-01 isolated from traditionally fermented peppers based on E-nose and GC-IMS. The results showed that E-nose could clearly distinguish the overall flavor differences of L. plantarum CL-01 under capsaicin stress. A total of 48 volatile compounds (VOCs) were characterized by means of GC-IMS, and the main VOCs belonged to acids and alcohols. Capsaicin stress significantly promoted L. plantarum CL-01 to produce alpha-pinene, ethyl crotonate, isobutyric acid, trans-2-pentenal, 2-methyl-1-butanol, 3-methyl-3-buten-1-ol, 1-penten-3-one, 2-pentanone, 3-methyl-1-butanol-D, and 2-heptanone (p < 0.05). In addition, under capsaicin stress, the contents of 1-penten-3-one, 3-methyl-3-buten-1-ol, 5-methylfurfuryl alcohol, isobutanol, 2-furanmethanethiol, 2,2,4,6,6-pentamethylheptane, 1-propanethiol, diethyl malonate, acetic acid, beta-myrcene, 2-pentanone, ethyl acetate, trans-2-pentenal, 2-methylbutyl acetate, and 2-heptanone produced by L. plantarum CL-01 were significantly increased along with the fermentation time (p < 0.05). Furthermore, some significant correlations were observed between the response values of specific E-nose sensors and effective VOCs.

Metabolomics and metatranscriptomics reveal the influence mechanism of endogenous microbe (Staphylococcus succinus) inoculation on the flavor of fermented chili pepper

This study integrated metabolomic and metatranscriptomic techniques to examine how the endogenous microbe, Staphylococcus succinus, influenced the essential flavor of fermented chili peppers. The mechanisms governing spontaneous fermentation and S. succinus-inoculated fermentation were also elucidated. Esters (e.g., ethyl undecanoate, isoamyl acetate, and methyl salicylate), terpenes (e.g., terpinen-4-ol), and alcohols (e.g., α-terpineol, linalool, and 4-methyl-3-heptanol) were found to be the key aroma-active compounds, aspartic acid (Asp) and glutamic acid (Glu) were identified as primary flavoring free amino acids. Notably, during the early stages of S. succinus-inoculated fermentation, the production of these essential metabolites was abundant, while their gradual increase over time was observed in the case of spontaneous fermentation. Metatranscriptomic analysis revealed that S. succinus inoculation could up-regulate genes related to glycolysis, amino acid metabolism, and aroma compound synthesis. These changes sequentially boosted the production of sweet and umami free amino acids, enhanced organic acid levels, increased unique aroma compound generation, and further improved the flavor and quality of the fermented chili peppers. Therefore, S. succinus inoculation can augment the sensory quality of fermented chili peppers, making this strain a promising candidate for Sichuan pickle fermentation starters.

Effect of inoculating Pichia spp. starters on flavor formation of fermented chili pepper: Metabolomics and genomics approaches

The influence of Pichia spp. on flavor formation and metabolic pathways during chili pepper fermentation was investigated in this study. Multiple omics approaches were employed, including metabolomics analysis to identify volatile and non-volatile flavor compounds, and genomic analysis to gain insights into the underlying molecular mechanism driving flavor formation of chili peppers inoculated with Pichia spp. The results showed that inoculation with Pichia spp. accelerated fermentation process of chili peppers compared to spontaneous fermentation. Metabolomics analysis showed P. fermentans promoted characteristic terpenes [e.g., (Z)-β-ocimene and linalool], L-glutamate, gamma-aminobutyric acid, and succinate production, while P. manshurica produced more alcohols (e.g., isoamyl alcohol and phenylethyl alcohol) and phenols (e.g., 4-ethylguaiacol and 2-methoxy-4-methylphenol). Genomics analysis revealed that a substantial portion of the genes in Pichia spp. were associated with amino acid and carbohydrate metabolism. Specifically, the pathways involved in amino acid metabolism and the release of glycoside-bound aromatic compounds were identified as the primary drivers behind the unique flavor of fermented chili peppers, facilitated by Pichia spp.

Changes in Yield-Related Traits, Phytochemical Composition, and Antioxidant Activity of Pepper (Capsicum annuum) Depending on Its Variety, Fruit Position, and Ripening Stage

The relationship between fruit position, ripening stage, and variety has not been well studied in pepper plants. To understand the interaction of these factors, a diversity of phytochemical traits as well as antioxidant activity were investigated with agronomic traits in eleven hot pepper varieties collected from the upper and lower parts of the plant and harvested at three maturity stages (green, orange, and red). Capsaicin content (CAP) showed a relatively high genetic effect; on the contrary, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity were more affected by the ripening stage and fruit position. The CAP values ranged from 0.29 ('FKbM') to 0.77 ('Bka') mg CAP equivalents g-1 DW. The ripening stage was the predominant factor for TPC, TFC, DPPH, and FRAP. There was no significant interaction between A × FP, A × RS, and FP × RS for all agro-morphological fruit traits. Variety, fruit position, and ripening stage effects are more significant than all interactions calculated. Lower fruit positions in all samples showed a maximum fruit size, whereas phytochemical traits and yield per plant were relevant in the upper parts, and Phytochemical traits and yield per plant were significantly correlated. From PCA and cluster analysis, all varieties showed the highest biochemical and antioxidant levels with moderate fruit size, except the 'Bel' variety that showed the smallest fruit traits with high yields, and the 'FKbM' and 'FKbK' varieties that showed the highest fruit size but low yields. This study supplies information to identify interesting cultivars with considerable levels of bioactive and phytochemical metabolites, which is useful for breeding programs of novel varieties.

Relationship between the Dynamics of Flavor Compounds and Microbial Succession in the Natural Fermentation of Zhalajiao, a Popular Traditional Chinese Fermented Chili Paste

Zhalajiao, a traditional Chinese fermented food, is popular due to its unique flavor. Traditional Zhalajiao fermentation is closely related to flavor compounds production. However, the mechanisms underlying the formation of these crucial flavor components in Zhalajiao remain unclear. Here, we explored the dynamic changes in physical and chemical properties, microbial diversity, and flavor components of Zhalajiao at various fermentation times. In total, 6 organic acids, 17 amino acids, and 21 key volatile compounds were determined as flavor components. In Zhalajiao, Lactobacillus and Cyanobacterium were the main bacteria that were involved in the formation of crucial flavor compounds. Candida showed a significant correlation with 14 key flavor compounds during fermentation (p < 0.05) and was the main fungal genus associated with flavor formation in Zhalajiao. This research offers a theoretical foundation for the flavor regulation and quality assurance of Zhalajiao.

Effect of Sichuan Pepper (Zanthoxylum genus) Addition on Flavor Profile in Fermented Ciba Chili (Capsicum genus) Using GC-IMS Combined with E-Nose and E-Tongue

This study examined the flavor profiles of fermented Ciba chili, comparing samples with Sichuan pepper (HJ) to those without Sichuan pepper (CK), using three analytical techniques: E-tongue, E-nose, and gas chromatography-ion mobility spectrometry (GC-IMS). The results obtained from the E-tongue and E-nose exhibited a clear difference in taste and flavor between CK and HJ. In detail, CK mainly exhibited a sour flavor profile, whereas HJ displayed an intricate and rich flavor. The HS-GC-IMS results identified a total of 60 compounds in the samples, with terpenes, alcohols, and esters being the primary volatile flavor compounds. Additionally, Zanthoxylum was found to significantly enhance the concentration of these compounds in fermented Ciba chili. Through robust principal component analysis (rPCA), 17 distinct flavor compounds were selected. Correlation analysis revealed that most terpenes exhibited positive correlations with LY2/LG, LY2/gCT1, LY2/Gct, LY2/G, LY2/Gh, and terpenes were found in higher concentrations in HJ. This study contributes a theoretical basis and provides data support for optimizing the fermentation process and elucidating the underlying mechanism of characteristic aroma formation in Ciba chili after fermentation.

Fully nondestructive analysis of capsaicinoids electrochemistry data with deep neural network enables portable system

Electrochemical methods have been extensively applied for the detection of chemical information from food or other analytes. However, existing electrochemical methods are limited to focusing solely on the absorption peaks and disregard much of the hidden chemical fingerprint information. Consequently, electrochemical sensors are constrained by their ability to detect samples containing multiple source-material mixtures with overlapping constituents. We hypothesized that the target substances can be effectively identified and detected using differential sensor data combined with artificial intelligence (AI). In this study, we developed a novel signal array composed of five metal electrodes and used a convolutional neural network (CNN) model for feature extraction to detect capsaicinoids in stews. Our results indicate that the proposed method achieved satisfactory predictions with a root mean square error (RMSE) of 5.407 in independent brine samples. This provides a promising strategy and practical approach for the nondestructive analysis of multidimensional electrochemical data of mixed analytes.

Capsaicinoids and volatile flavor compounds profile of Sichuan hotpot as affected by cultivar of chili peppers during processing

Sichuan hotpot oil is a distinctive traditional Chinese cuisine, and chili pepper is an essential material for its flavor formation. In this study, the effect of chili pepper cultivars on capsaicinoids as well as Sichuan hotpot oil volatile compounds were examined. Gas chromatography-mass spectrometry (GC-MS) and chemometrics were employed to ascertain the differences between volatile components and flavor. The results showed that the EJT hotpot oil had the highest color intensity of 34.8, and the SSL hotpot oil had the highest capsaicinoids content of 1.536 g/kg. The results of QDA showed distinct differences among hotpot oils in terms of all sensory properties. A total of 74 volatile components were detected. Aldehydes, ketones, esters, and acids were the dominant volatile compounds formed in 18 hotpot oil samples and showed a significant difference, suggesting that they played a key role in flavor contribution and distinguishing the flavor differences between different hotpot oils. The PCA results well distinguished 18 kinds of hotpot oil.

Improvement of physicochemical characteristics, flavor profiles and functional properties in Chinese radishes via spontaneous fermentation after drying

Spontaneously dried-fermented radishes have been consumed in China for hundreds of years and are usually fermented for a long time to acquire high quality. In this study, the spontaneously dried-fermented radishes with short-term manufacturing periods were made from five different varieties of radishes that grew in the same environment. In addition, the physicochemical characteristics (i.e., moisture content, soluble solid, and pH value), flavor profiles (i.e., free amino acids, organic acids, and volatile compounds), and functional properties (i.e., total phenolics content, total flavonoids content, sulforaphane content, and γ-aminobutyric acid [GABA] content) of these five raw radishes and spontaneously dried-fermented radishes were analyzed and compared. In detail, the content of volatile and nonvolatile compounds increased, especially in oxalic acid, succinic acid, and umami free amino acids. Furthermore, functional components, such as sulforaphane and GABA, were also enriched via spontaneous fermentation after drying. In addition, the results of principal component analysis, hierarchical clustering analysis, and redundancy analysis showed that there were significant discrepancies appeared when raw radishes were processed via spontaneous fermentation or not. These results suggested that the process of spontaneous fermentation after drying may contribute to improving the quality of fresh radishes. Notably, radishes with red skin and flesh were regarded as exceptional varieties for processing, because of the preferable flavor profiles and affluent functional substances via spontaneous fermentation after drying. Therefore, these findings could deliver a systematical insight into developing processed radishes with high quality. PRACTICAL APPLICATION: The spontaneously dried-fermented radishes were manufactured through the process of spontaneous fermentation after drying, which acquired tasty and healthy characteristics by accumulating the volatile and nonvolatile compounds as well as the functional components, like total phenolics, total flavonoids, sulforaphane, and γ-aminobutyric acid. Importantly, because of the excellent processing properties, the radishes with red skin and flesh could be more appropriate to produce spontaneously dried-fermented radishes. Our findings may provide a practical strategy for developing vegetable relishes with superb flavor profiles and good functional properties in pickled vegetables.

Flavor production in fermented chayote inoculated with lactic acid bacteria strains: Genomics and metabolomics based analysis

In this study, genomics and metabolomics were combined to reveal possible bio-synthetic pathways of core flavor compounds in pickled chayote via lactic acid bacteria (LAB) fermentation. The Lactiplantibacillus plantarum, Levilactobacillus brevis, and Lacticaseibacillus paracasei were selected as core LAB strains with better flavor-producing ability for chayote fermentation. The genomic results showed L. plantarum contained the largest number of metabolism annotated genes, while L. brevis had the fewest. Besides, the largest number of volatile compounds was detected in chayote fermented by L. plantarum, followed by L. brevis and L. paracasei. Some unique odor-active compounds (aldehydes, esters, and alcohols) and taste-active compounds (amino acids and dipeptides) were produced by different LAB strains. Accordingly, phenylalanine metabolic pathway (M00360), amino acid metabolic decomposition pathway (the Ehrlich pathway) and the anabolic pathway (the Harris pathway), and fatty acid biosynthesis pathway (M00061) were the main biosynthesis pathway involved in the flavor formation via LAB fermentation.

Effects of Brines and Containers on Flavor Production of Chinese Pickled Chili Pepper (Capsicum frutescens L.) during Natural Fermentation

The effects of (fresh/aged) brine and (pool/jar) containers on the flavor characteristics of pickled chili peppers were investigated based on a multivariate analysis integrated with kinetics modeling. The results showed that the effect of brine on organic acid, sugar, and aroma was more dominant than that of containers, while free amino acids production was more affected by containers than brines. Chili pepper fermented using aged brine exhibited higher acidity (3.71−3.92) and sugar (7.92−8.51 mg/g) than that using fresh brine (respective 3.79−3.96; 6.50−9.25 mg/g). Besides, chili peppers fermented using pool containers showed higher free amino acids content (424.74−478.82 mg/100 g) than using a jar (128.77−242.90 mg/100 g), particularly with aged brine. As for aroma, the number of volatiles in aged brine was higher (88−96) than that in fresh brine (76−80). The contents of the esters, alcohols, and ketones were significantly higher in the aged brine samples than those in fresh brine (p < 0.05), while terpenes in chili pepper fermented using the pool were higher than those using the jar. In general, jar fermentation with aged brine contributed more flavor to pickled chili peppers than other procedures.

The Influence of Lactic Acid Fermentation on Selected Properties of Pickled Red, Yellow, and Green Bell Peppers

Red, yellow, and green peppers are vegetables rich in natural pigments. However, they belong to seasonal vegetables and need to be treated to prolong their shelf life. One new approach to processing vegetables is to pickle them using lactic acid bacteria. The use of such a process creates a new product with high health value, thanks to the active ingredients and lactic acid bacteria. Therefore, this study aimed to evaluate the effect of the applied strain of lactic acid bacteria (LAB) on the chemical properties, including the content of active compounds (pigments) and the physical properties of the peppers. Levilactobacillus brevis, Limosilactobacillus fermentum, and Lactoplantibacillus plantarum were used for fermentation and spontaneous fermentation. The pigments, polyphenols content, and antioxidant properties were determined in the pickled peppers, as well as sugar content, color, dry matter, texture properties, and the count of lactic acid bacteria. In all samples, similar growth of LAB was observed. Significant degradation of chlorophylls into pheophytins was observed after the fermentation process. No significant differences were observed in the parameters tested, depending on the addition of dedicated LAB strains. After the fermentation process, the vitamin C and total polyphenols content is what influenced the antioxidant activity of the samples. It can be stated that the fermentation process changed the red bell pepper samples in the smallest way and the green ones in the highest way.

Impact of Inoculating with Indigenous Bacillus marcorestinctum YC-1 on Quality and Microbial Communities of Yibin Yacai (Fermented Mustard) during the Fermentation Process

Bacillus species play an important role in improving the quality of some fermented foods and are also one of the dominant bacteria in Yibin Yacai (fermented mustard). However, little is known about their effects on the quality of Yibin Yacai. Here, the effect of Bacillus marcorestinctum YC-1 on the quality and microbial communities of Yibin Yacai during the fermentation process was investigated. Results indicated that the inoculation of Bacillus marcorestinctum YC-1 promoted the growth of Weissella spp. and Lactobacillus spp. and inhibited the growth of pathogens, accelerating the synthesis of free amino acids and organic acids and the degradation of nitrite. Furthermore, inoculating Yibin Yacai with YC-1 could effectively enhance the synthesis of alcohols and terpenoids in yeasts, thus producing more linalool, terpinen-4-ol, and α-muurolen in Yibin Yacai, and endowing it with pleasant floral, fruity, woody, and spicy aromas. These findings reveal that the inoculation of B. marcorestinctum YC-1 can improve the quality and safety of Yibin Yacai by changing microbial communities as fermentation proceeds.

Volatile Flavor Profile and Sensory Properties of Vegetable Soybean

The volatile flavor profiles and sensory properties of different vegetable soybean varieties popularized and cultivated in China for 20, 10, and 2 years (TW292, X3, and SX6, respectively) were investigated. Nutrient composition analysis revealed that TW292 had a high soluble protein and soluble sugar content but low fat content. The total free amino acid content (15.43 mg/g) and umami free amino acid content (6.08 mg/g) of SX6 were significantly higher (p < 0.05) than those of the other varieties. An electronic tongue effectively differentiated between the umami and sweetness characteristics of the vegetable soybeans. Differences in sensory evaluation results were mainly reflected in texture and taste. A total of 41 volatile compounds were identified through HS-SPME-GC-MS, and the main flavor compounds were 1-octen-3-ol, hexanal, (Z)-2-heptenal, 2-octene, nonanal, (Z)-2-decenal, and 3,5-octadien-2-one. However, the volatile composition of different vegetable soybean varieties exhibited large variability in type and relative contents. Considerable differences in nutritional, organoleptic, and aroma characteristics were found among different varieties. The results of this study will provide a good basis for the assessment and application of the major vegetable soybean varieties grown in China.