The potential of kiwifruit puree as a clean label ingredient to stabilize high pressure pasteurized cloudy apple juice during storage

Inactivated mechanisms of high pressure processing combined with mild temperature on pectin methylesterase and its inhibitor

High pressure processing (HPP) of orange juice faces storage issues due to refrigeration need and cloud loss caused by pectin methylesterase (PME). Our previous research indicated that HPP conjunction with pectin methylesterase inhibitor (PMEI) enhanced juice stability, but not fully inactivated PME. This study explored the effectiveness of HPP with mild temperature treatments to fully inactivate PME and sterilize microorganisms in juice, using experimental analysis and molecular dynamics simulation. The findings revealed that PME activity was reduced by 94 % at 600 MPa and 60 °C, with completely inactivating at 80 °C. Conversely, PMEI exhibited resistance to pressure and temperature. Following processes at 600 MPa and above 60 °C, the tail-end helix structure of PME destabilized, with α-helices converting to β-sheets and disrupting hydrogen bonds within molecular chain. Conversely, the structure of PMEI was stable. Additionally, the combination of HPP and temperature treatment enhanced the binding affinity between PME and PMEI.

Enhancing fermented vegetable flavor with Lactobacillus plantarum and Rhodotorula mucilaginosa

The formation of flavor in fermented vegetables is directly associated with the interactions among the resident microbial strains. This study explored the cooperative dynamics between Lactobacillus plantarum and Rhodotorula mucilaginosa in a simulated cabbage juice system. The obtained results indicated that the co-cultivation of these strains accelerated fermentation kinetics and enhanced lactic acid production. The strains achieved a balanced consumption of substrates within the co-fermentation system through the exchange of metabolites. Additionally, co-fermentation facilitated the synthesis of characteristic flavor compounds while reducing the levels of undesirable flavors. Growth monitoring and transcriptomic analysis revealed that L. plantarum, as the dominant strain, perceived the surrounding environment through quorum sensing signals and upregulated genes related to the synthesizing of key compounds, enhancing product yields and forming biofilms to adapt to the symbiotic environment. Conversely, R. mucilaginosa responded to the stress induced by L. plantarum via upregulating transporters of metabolites, genes related to antioxidant stress, and longevity regulating, ultimately achieving coexistence with L. plantarum. This research provides a comprehensive understanding of the interplay between microbial strains in modulating fermentation processes and flavor profiles in vegetable fermentation.

Exploration of changes in sensory, physicochemical properties and microbial metabolic activities of grass carp meat with five thermal processing treatments during refrigerated storage

This study aimed to employed the effects of five thermal processing methods, namely steaming (SM), boiling (BO), frying (FY), roasting (RO), and vacuum sealing (SV), on the sensory, physicochemical properties, and microbial composition of grass carp meat during refrigerated storage, alongside unheated raw meat (RW) as control. The results showed that thermal treatment improved the sensory quality and shelf life of refrigerated grass carp meat, and their shelf life was RW < BO Collapse

Key Words

• Correlation analysis
• Grass carp
• Microbial metabolism
• Refrigeration
• Thermal processing

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Affiliation(s)

Lu Zhang National R&D Center for Freshwater Fish Processing, College of Life Sciences, Jiangxi Normal University, Nanchang, Jiangxi 330022, China School of Health, Jiangxi Normal University, Nanchang, Jiangxi 330022, China
Yaqin Yu National R&D Center for Freshwater Fish Processing, College of Life Sciences, Jiangxi Normal University, Nanchang, Jiangxi 330022, China
Chunming Tan School of Health, Jiangxi Normal University, Nanchang, Jiangxi 330022, China
Shi Nie National R&D Center for Freshwater Fish Processing, College of Life Sciences, Jiangxi Normal University, Nanchang, Jiangxi 330022, China
Qinghui Wen School of Health, Jiangxi Normal University, Nanchang, Jiangxi 330022, China
Zongcai Tu National R&D Center for Freshwater Fish Processing, College of Life Sciences, Jiangxi Normal University, Nanchang, Jiangxi 330022, China School of Health, Jiangxi Normal University, Nanchang, Jiangxi 330022, China Nanchang University, Nanchang, Jiangxi 330006, China

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Inactivation mechanisms on pectin methylesterase by high pressure processing combined with its recombinant inhibitor

High pressure processing (HPP) juice often experiences cloud loss during storage, caused by the activity of pectin methylesterase (PME). The combination of HPP with natural pectin methylesterase inhibitor (PMEI) could improve juice stability. However, extracting natural PMEI is challenging. Gene recombination technology offers a solution by efficiently expressing recombinant PMEI from Escherichia coli and Pichia pastoris. Experimental and molecular dynamics simulation were conducted to investigate changes in activity, structure, and interaction of PME and recombinant PMEI during HPP. The results showed PME retained high residual activity, while PMEI demonstrated superior pressure resistance. Under HPP, PMEI's structure remained stable, while the N-terminus of PME's α-helix became unstable. Additionally, the helix at the junction with the PME/PMEI complex changed, thereby affecting its binding. Furthermore, PMEI competed with pectin for active sites on PME, elucidating. The potential mechanism of PME inactivation through the synergistic effects of HPP and PMEI.

High-Pressure Processing Effects on Microbiological Stability, Physicochemical Properties, and Volatile Profile of a Fruit Salad

Nowadays, consumers are more aware of the effects of their diet on their health, and thus demand natural or minimally processed food products. Therefore, research has focused on processes that assure safe products without jeopardizing their nutritional properties. In this context, this work aimed to evaluate the effects of high-pressure processing (550 MPa/3 min/15 °C, HPP) on a fruit salad (composed of melon juice and pieces of Golden apple and Rocha pear) throughout 35 days of storage at 4 °C. For the physicochemical properties analysed (browning degree, polyphenol oxidase activity, antioxidant activity (ABTS assay), and volatile profile), a freshly made fruit salad was used, while for the microbiological tests (total aerobic mesophiles, and yeast and moulds) spoiled melon juice was added to the fruit salad to increase the microbial load and mimic a challenge test with a high initial microbial load. It was determined that processed samples were more microbiologically stable than raw samples, as HPP enabled a reduction of almost 4-log units of both total aerobic mesophiles and yeasts and moulds, as well as an almost 1.5-fold increase in titratable acidity of the unprocessed samples compared to HPP samples. Regarding browning degree, a significant increase (p < 0.05) was observed in processed versus unprocessed samples (roughly/maximum 68%), while the addition of ascorbic acid decreased the browning of the samples by 29%. For antioxidant activity, there were no significant differences between raw and processed samples during the 35 days of storage. An increase in the activity of polyphenol oxidase immediately after processing (about 150%) was confirmed, which was generally similar or higher during storage compared with the raw samples. Regarding the volatile profile of the product, it was seen that the compounds associated with melon represented the biggest relative percentage and processed samples revealed a decrease in the relative quantity of these compounds compared to unprocessed. Broadly speaking, HPP was shown to be efficient in maintaining the stability and overall quality of the product while assuring microbial safety (by inactivating purposely inoculated microorganisms), which allows for longer shelf life (7 versus 28 days for unprocessed and processed fruit salad, respectively).

Effect of Rhodotorula mucilaginosa inoculation on the aroma development of a fermented vegetables simulated system

Fermented vegetables are known for their unique flavors and aromas, which are influenced by the complex microbial processes that occur during fermentation. Rhodotorula mucilaginosa is a red yeast strain that is frequently isolated from fermented vegetables. However, the specific mechanisms underlying their effects on aroma production remain unclear. In this study, a simulated system of vegetables fermented using vegetable juices was used to investigate the effects of R. mucilaginosa inoculation on aroma development. The results demonstrated that this red yeast strain could utilize the nutrients present in the vegetable juices to support its growth and reproduction. Moreover, the inoculation of fermented vegetable juices with this yeast strain led to an increase in the levels of umami amino acids and sweet amino acids. Furthermore, this yeast strain was found able to significantly reduce the content of sulfur-containing compounds, which may decrease the unpleasant odor of fermented vegetables. Additionally, the yeast strain was capable of producing high concentrations of aromatic compounds such as phenylethyl alcohol, methyl 2-methylbutyrate, methyl butyrate, and nonanoic acid in a minimum medium. However, only phenylethyl alcohol has been identified as a core aromatic compound in fermented vegetable juice. The three fermented vegetable juices exhibited significantly different flavor profiles according to comparative analysis. Therefore, the core flavor compounds found in fermented vegetables are primarily derived from the release and modification of endogenous flavors naturally present in the vegetables, facilitated by the yeast during fermentation.

The impact of different drying methods on the physical properties, bioactive components, antioxidant capacity, volatile components and industrial application of coffee peel

This study evaluated the effects of hot air drying (HAD), microwave drying (MD), vacuum drying (VD), sun drying (SD) and vacuum freeze drying (VFD) on the physical properties, bioactive components, antioxidant capacity, volatile components and industrial application of coffee peel. The results showed VFD could retain the appearance color, total phenolics (19.49 mg GAE/g DW), total flavonoids (9.65 mg CE/g DW), caffeine (3.15 mg/g DW), trigonelline (2.71 mg/g DW), and antioxidant capacities of fresh sample to the greatest extent, but its operating cost was significantly higher than other treatments and total volatile components were in the minimum levels. HAD and SD exhibited the highest loss rates of total phenols and antioxidant capacities, exceeding 50%. MD offered the lowest operating cost, superior retention of bioactive components, and the richest variety and quantity of volatile compounds. Therefore, it is recommended to use MD to dehydrate the coffee peel in actual production.

Effect of high hydrostatic pressure treatment on the inactivation and sublethal injury of foodborne pathogens and quality of apple puree at different pH

The objectives of this study were to evaluate the survival of high hydrostatic pressure (HHP)-treated Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes in apple puree, as well as to determine the levels of HHP-induced cell injury according to the pressure level, holding time, and pH of apple puree. Apple puree was inoculated with three foodborne pathogens and treated at pressures of 300-600 MPa for up to 7 min at 22 °C using HHP equipment. Increasing the pressure level and lowering the pH of apple puree led to larger microbial reductions, and E. coli O157:H7 showed higher resistance compared to S. Typhimurium and L. monocytogenes. Besides, approximately 5-log injured cells of E. coli O157:H7 were induced in apple puree at pH 3.5 and 3.8. HHP treatment at 500 MPa for 2 min effectively achieved complete inactivation of the three pathogens in apple puree at pH 3.5. For apple puree at pH 3.8, more than 2 min treatment of HHP at 600 MPa is seemingly needed to achieve complete inactivation of the three pathogens. Transmission electron microscopy analysis was conducted to identify ultrastructural changes in the injured or dead cells after HHP treatment. Plasmolysis and uneven cavities in the cytoplasm were observed in injured cells, and additional deformations, such as distorted and rough cell envelopes, and cell disruption occurred in dead cells. No changes in solid soluble content (SSC) and color of apple puree were observed after HHP treatment, and no differences were detected between control and HHP-treated samples during 10 d of storage at 5 °C. The results of this study could be useful in determining the acidity of apple purees or the treatment time at specific acidity levels when applying the HHP processing.

A Novel Strategy to Improve Cloud Stability of Orange-Based Juice: Combination of Natural Pectin Methylesterase Inhibitor and High-Pressure Processing

This study investigated the prospect of producing cloud-stable orange-based juice by combining high-pressure processing (HPP) with a natural kiwifruit pectin methylesterase inhibitor (PMEI) during chilled storage. Kiwifruit is rich in a PMEI, which greatly improves the cloud loss caused by the pectin methylesterase (PME) demethylation of pectin. The results show that the cloud loss of orange juice occurred after 3 days, while the orange-kiwifruit mixed juice and kiwifruit puree were cloud stable during 28 days' storage. Although, the kiwifruit puree contained larger particles compared to the orange juice, its higher viscosity and solid-like behavior were dominant, improving the cloud stability of the juice systems. In addition, the particle size distribution and rheological properties were highly related to PME activity, PMEI activity, and pectin characterization. The kiwifruit PMEI showed higher resistance to HPP and storage time than PME. More water-solubilized pectin fractions with a high molecular mass were found in the kiwifruit puree, leading to its high viscosity and large particle size, but a more chelator-solubilized pectin fraction with a low esterification degree was observed in the orange juice, resulting in its cloud loss. In general, the outcome of this work provides a novel strategy to improve the cloud stability of orange-based juices using natural PMEIs and nonthermal processing technologies.

Role of pectin characteristics in orange juice stabilization: Effect of high-pressure processing in combination with centrifugation pretreatments

"High-pressure processing (HPP) plus" combined technologies are applied to overcome the limitation of single HPP and to produce juices with more stable quality during storage. This research explored the potential of HPP in combination with centrifugation to produce cloud stable orange juice during refrigerated storage. The results indicated that HPP combined processing technology significantly improved the cloud stability of orange juice, which was related to removed large particles, reduced viscosity, decreased protein contents, and inactivated pectin methylesterase activity induced by centrifugation (P < 0.05). Besides, chelator solubilized pectin (CSP) decreased but water solubilized pectin (WSP) maintained in the juice after centrifugation. During storage, the conversion of pectin fraction from WSP to CSP, resulting in sedimentation appeared in centrifugation treated orange juice when stored for 28 days. In general, pectin characteristics changes and pectin fractions conversion were the main driving forces affecting cloud stability of orange juice pasteurized by HPP in combination with centrifugation and during chilled storage.

Dynamics of microbial communities, flavor, and physicochemical properties of pickled chayote during an industrial-scale natural fermentation: Correlation between microorganisms and metabolites

Pickled chayote is a Chinese fermented vegetable with unique flavors and is favored by local consumers. However, little is known about its quality changes and microbial community succession during fermentation and the relationship between microbes and quality. In the work, the physicochemical quality attributes (pH, acidity, nitrite, texture, and color) and flavor properties (sugars, organic acids, free amino acid [FAA], and volatiles) were investigated. The results revealed that organic acids, FAAs, and key volatiles (esters, terpenes, alcohols, and phenols) significantly increased during fermentation. Lactobacillus was the dominant bacterial genus with Lactobacillus alimentarius being the prevalent species; Kazachstania and Pichia were dominant fungal genera with Kazachstania humilis and Pichia membranifaciens being the prevalent species. The microbial metabolic network found that bacteria (L. alimentarius, L. futsaii, and L. paralimentarius) and fungi (K. humilis and P. membranifaciens) played significant roles in the physicochemical changes and flavor production of pickled chayote.

Effect of centrifugal pre-treatment on flavor change of cloudy orange juice: Interaction between pectin and aroma release

Cloud loss of orange juice could be effectively inhibited by centrifugal treatment, but it can induce flavor changes, which become a new challenge for the industry. This work aims to investigate the effect of centrifugation on flavor changes in orange juice and explore its possible mechanism. Taste- and aroma-related attributes were analyzed, and pectin was characterized. Results indicated that pH (4.00), total soluble solid (9.67 °Brix), titratable acidity (0.42%), sucrose (44%), fructose (29%), and glucose (27%) were less affected by centrifugation (P > 0.05). However, aroma compounds significantly changed (P < 0.05), where terpenes and alcohols tended to be distributed in pulp and serum after centrifugation, respectively. Pearson correlation analysis showed that aroma compound distribution induced by centrifugation was highly related to chelator-solubilized pectin fraction and sodium carbonate-solubilized pectin fraction (|R| > 0.9). In general, centrifugation clearly changed aroma of orange juice, which was mainly affected by pectin characteristics.

Evaluation of quality changes of differently formulated cloudy mixed juices during refrigerated storage after high pressure processing

Cloudy fruit and vegetable mixed juice (MJ) pasteurized by high pressure processing (HPP) showed an increasing market demand. However, browning, sedimentation, and flavor changes of HPP juice during storage have been a great challenge for the beverage industry. The aim of this work was to investigate quality changes of HPP MJs during storage and to explore the potential to create the shelf-stable MJs with fresh-like organoleptic quality through HPP. In the work, commercial MJ1 (orange, mango, and kiwifruit) and MJ2 (carrot and pineapple) were formulated and their quality changes during storage were investigated. The results indicated no visible color changes and sedimentation were observed in MJ1 and MJ2 during refrigerated storage (90 days). However, sucrose decreased as glucose and fructose increased; a large number of aldehydes and alcohols decreased but some terpenoids increased during storage. In general, blending proper fruit and vegetable to produce MJs combing with HPP could maintain high cloud and color stability, but sugars and volatiles clearly changed during storage.

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HPP mixed juice showed high color and cloud stability during chilled storage.

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Aldehydes and alcohols decreased but terpenoids increased during storage.

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Sucrose decreased with glucose and fructose increasing during storage.

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Carrot-pinapple mixed juice showed high quality stability during storgae.

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

This work monitored the effect of ripening and variety on the physiochemical quality and flavor of fermented Chinese chili pepper (Paojiao). Three commercial varieties of chili pepper (Capsicum frutescens Linn.) at three ripening stages were selected. Physiochemical quality (color, texture, and vitamin C) and flavor properties [capsaicinoids, free amino acid (FAA), and aroma] were determined and compared by multivariate data analysis. The hardness and chewiness decreased, while the contents of vitamin C, capsaicin, and taste-active FAAs increased in Paojiao with ripening. More volatiles were found in green peppers. Fingerprinting and multivariate data analysis revealed that ester, aldehydes, and terpenes were discriminant volatiles that significantly changed in Paojiao during ripening. In general, ripening and variety greatly affect the physiochemical and flavor quality of peppers and their effects intensify after fermentation.

Impacts of thermal and non-thermal processing on structure and functionality of pectin in fruit- and vegetable- based products: A review

Pectin, a major polysaccharide found in the cell walls of higher plants, plays major roles in determining the physical and nutritional properties of fruit- and vegetable-based products. An in-depth understanding of the effects of processing operations on pectin structure and functionality is critical for designing better products. This review, therefore, focuses on the progress made in understanding the effects of processing on pectin structure, further on pectin functionality, consequently on product properties. The effects of processing on pectin structure are highly dependent on the processing conditions. Targeted control of pectin structure by applying various processing operations could enhance textural, rheological, nutritional properties and cloud stability of products. While it seems that optimizing product quality in terms of physical properties is counteracted by optimizing the nutritional properties. Therefore, understanding plant component biosynthesis mechanisms and processing mechanisms could be a major challenge to balance among the quality indicators of processed products.

Evaluation of the physiochemical and aromatic qualities of pickled Chinese pepper (Paojiao) and their influence on consumer acceptability by using targeted and untargeted multivariate approaches

Paojiao, which is traditionally pickled Chinese chili peppers (Capsicum frutescens Linn.), possesses unique flavors. This study was conducted to investigate the flavor, mouthfeel, and consumer acceptability of Paojiao. The quality of six homemade and two industrial Paojiao samples were evaluated by integrating untargeted (to fingerprint volatile fraction) and targeted (to analyze free amino acids or FAAs, capsaicinoids, and texture) approaches. Furthermore, multivariate data analysis (MVDA) was applied to identify the quality characteristics that drive the consumer acceptability for Paojiao. As for the targeted quality, hardness (1.30-10.52 N) and capsaicin (2.22-3.84 mg/g) varied with different samples. The main taste-active FAAs in Paojiao were detected. A total of 127 volatiles were observed, and esters were the major components. Based on sensory analysis, the homemade samples received higher acceptability than the industrial samples. MVDA demonstrated that some key volatiles, taste-active FAAs, and chewiness were the discriminant quality attributes affecting consumer acceptability.

Effects of Hot-Water Extract from Vine Tea (Ampelopsis grossedentata) on Acrylamide Formation, Quality and Consumer Acceptability of Bread

Acrylamide is a harmful substance that could be inhibited by natural products. Vine tea is an edible herb belonging to the Vitaceae family and has been approved by Chinese authorities as a new food ingredient in 2013. However, the effects of vine tea extract on acrylamide formation and bread quality are rarely investigated. In this study, the polyphenol composition of hot-water extract from vine tea was characterized by ultrahigh-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-ESI-HRMS/MS), and its effects on acrylamide formation, quality, and consumer acceptability of bread were investigated. Vine tea extract and its main polyphenol, dihydromyricetin, significantly inhibited the acrylamide formation in bread, especially the low dose of vine tea extract (1.25 g/kg), which decreased the acrylamide formation by 58.23%. The color and texture of bread were significantly affected by vine tea extract or dihydromyricetin, whereas the moisture content was not changed remarkably. Triangle and paired preference tests indicated that, although the aroma, appearance, and taste of the bread with vine tea extract significantly differ from those of the control bread, vine tea extract did not significantly affect the consumer acceptability. In conclusion, the addition of vine tea extract could be used to develop a new and healthy bread product with low acrylamide content.

Encapsulation of Lutein in Nanoemulsions Stabilized by Resveratrol and Maillard Conjugates

Lutein is incorporated into foods as a natural yellow pigment and nutraceutical. The introduction of lutein into many foods and beverages, however, is problematic because of its strong hydrophobicity and poor chemical stability. In this research, lutein-loaded nanoemulsions were prepared to overcome this problem. Casein-dextran Maillard conjugates or physical complexes were utilized as emulsifiers, while either medium chain triglycerides (MCT) or grape seed oil (GSO) were used as carrier oils. The impact of resveratrol addition on nanoemulsion stability was also examined. The influence of storage temperature, pH, and CaCl₂ concentration on the chemical and physical stability of the nanoemulsions was measured. The casein-dextran conjugates were highly effective at improving the physical resistance of the nanoemulsions to environmental stresses, but had a detrimental effect on their color stability. Conversely, nanoemulsions prepared from casein-dextran physical complexes were unstable around the protein's isoelectric point (pH 4.6), as well as upon addition of CaCl₂ . Incorporation of resveratrol and GSO into the nanoemulsions decreased lutein degradation and color fading at all temperatures. This study shows that casein-dextran conjugates are highly effective at improving the physical stability of lutein-loaded nanoemulsions, while resveratrol and GSO are effective at improving their chemical stability. PRACTICAL APPLICATION: Lutein can be used by the food industry to create "clean label" and functional food products. The major challenges in incorporating lutein in foods are its poor chemical stability and its high hydrophobicity, which makes it difficult to incorporate. Emulsion-based delivery systems assembled from natural ingredients may address these challenges. In this study, the impact of Maillard conjugates fabricated from caseinate and dextran, as well as resveratrol addition, on the formation and stability of lutein-enriched nanoemulsions was determined. The information obtained from this study will help the formulation of more effective functional foods and beverage products.