Changes in cell wall neutral sugar composition related to pectinolytic enzyme activities and intra-flesh textural property during ripening of ten apricot clones

Four distinct pathways involved in a "tug-of-war" lead to the non-linear nature of phenolic chemistry during lactic acid fermentation of fruits and vegetables

Introduction Lactic acid fermentation of fruits and vegetables (F&V) is endowed with new nutrients and flavors. "Phenolics" is a hot spot in this area, which evolve irregularly during fermentation. However, the mechanism about this non-linear phenomenon has been poorly understood.Objectives This paper was aimed at decoding the mechanism about the non-linear nature of phenolic chemistry during lactic acid fermentation of F&V.Methods Mango and cress slurries were fermented by Lactiplantibacillus plantarum. Different fractions of the slurry samples were analyzed comprehensively. Four pathways relating to phenolic changes were extracted, including adsorption of free phenolics by F&V cell wall materials, microbial adsorption and biotransformation of free phenolics, destabilization of covalent bond between bound phenolics and F&V cell walls. The in-depth features of each pathway during fermentation were explored by multidisciplinary methodologies.Results Throughout both fermentation of mango and cress slurries, free phenolics and the F&V cell wall components undergo dynamic changes. Due to the reduction of pectin fraction in the F&V cell walls during fermentation, the adsorption of free phenolics by F&V cell wall materials through surface diffusion was improved. Also, microbial cells, especially in the latter stages of fermentation, were capable of adsorbing free phenolics through surface diffusion. Moreover, the padC and bglB genes encoding phenolic acid decarboxylase and β-glucosidase were expressed during fermentation, contributing to the conversion of free phenolics. Besides, bound phenolics were not released during fermentation, although its covalent was weakened. The features of the above pathways vary with the fermentation stages and the composition of F&V components, resulting in non-linear changes of free phenolics during F&V fermentation. Conclusion F&V cell wall adsorption, microbial adsorption, microbial biotransformation, and destabilization of the covalent bond of bound phenolics compete in a dynamic "tug-of-war", leading to non-linear nature of phenolic chemistry during F&V fermentation.

Three-dimensional mass transfer modeling and phenolic chemistry exploration for ultrasound-assisted and microwave drying of goji berry

Herein, goji berries were pretreated with sodium carbonate (Na2CO3) and then dried via ultrasound-assisted air drying or microwave drying. Water migration and phenolic chemistry of goji berries were studied under drying. A three-dimensional ellipsoid water transport model, accounting for porosity and temperature fluctuations, was established to explore the intricacies of the drying mechanism. Generally, microwave drying promoted interior water transport compared to ultrasound drying. Among all the drying methods, microwave drying at 240 W (MW-240 W) exhibited the highest De (from 7.34 × 10-9 to 9.61 × 10-9 m2/s) and kc (6.78 × 10-4 m/s) values. The goji berries received a considerably high water content gradient between its surface and center within the first 2 s of all the drying treatments. Microwave drying diminished the water content gradient earlier than air drying and ultrasound-assisted air drying treatments. Furthermore, most correlations observed among phenolics, oxidase activity, and cell wall pectin did not align with the established theories, highlighting the highly nonlinear nature of phenolic chemistry during goji berry drying. This study provides a three-dimensional model to study the mass transfer mechanism of goji berries and analyzes the evolution of polyphenols during the drying process.

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 Various Flavors of Baijiu on the Microbial Communities, Metabolic Pathways, and Flavor Structures of Dongbei Suancai

This study aimed to assess the effects of Chinese Baijiu with different flavors as supplementary material on microbial communities and flavor formation during inoculated fermentation of Chinese Dongbei Suancai. The results showed that the addition of Fen flavor Baijiu significantly increased the relative abundance of Candida, Luzhou flavor Baijiu increased the relative abundance of Pedobacter and Hannaella, while Maotai flavor Baijiu increased the Chryseobacterium and Kazachstania. A total of 226 volatile metabolites were detected in Suancai fermented when adding different flavors of Baijiu. Furthermore, the significantly upregulated metabolites (p < 0.01) of Suancai after adding Baijiu increased by 328.57%, whereas the significantly downregulated metabolites decreased by 74.60%. Simultaneously, the addition of Baijiu promoted the synthesis and decomposition of amino acids and short-chain fatty acids in the early and middle stages of fermentation. Further, Maotai flavor Baijiu improved the diversification of metabolic pathways in the late stage of Suancai fermentation. The E-nose response showed that sulfur-organic, broad-alcohol, sulfur-chlor was the principal differential flavor in Suancai caused by adding Baijiu with different flavors. Simultaneously, Fen flavor Baijiu and Luzhou flavor Baijiu accelerated the formation of the Suancai flavor. These results indicated that Baijiu with different flavors had significant effects on the flavor formation of inoculated fermented Suancai.

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.

Effects of inoculation with a binary mixture of Lactobacillus plantarum and Leuconostoc citreum on cell wall components of Chinese Dongbei suancai

This study aimed to investigate the effects of inoculation with a starter culture consisting of Lactobacillus plantarum LNJ002 and Leuconostoc citreum BNCC 194779 on microbial community, cell wall polysaccharide characteristics, cell wall degrading enzymes, and microstructure during Chinese Dongbei suancai fermentation. The results showed that Lactobacillus (98.75%) was the dominant genus during fermentation of Dongbei suancai. The principal coordinates analysis (PCoA) suggested that inoculation with Lactobacillus promoted the stability of microbial community structure during Chinese Dongbei suancai fermentation. Besides, the lower content in cellulose (80.28 ± 2.61 ug/mg) and pectin (53.56 ± 2.67 ug/mg) observed in the inoculated fermented suancai. Simultaneously, the inoculated fermented suancai had the most decreases in SR 1 (70.35%) and SR 3 (72.06%) and the most increase in SR 2 (950%), which suggested that inoculation intensified the decrease of the linearity and the RG-1 branching degree of pectin. The contents of polygalacturonase (PG) and pectin methylesterase (PME) in inoculated fermented suancai were 21.06% and 21.86% higher than those in naturally fermented suancai. In addition, the surface of suancai leaves gradually changed from smooth to rough during fermentation, which was accelerated by inoculation. Moreover, Lactobacillus, Aspergillus, Wallemia and Mucor were all negatively correlated with cellulose and GalA. These results revealed that inoculation promoted the formation of dominant genus structure during suancai fermentation, changed the effects of enzymes on the degradation of cell wall components, thereby accelerated the formation of Chinese Dongbei suancai texture.

Potential role of cell wall pectin polysaccharides, water state, and cellular structure on twice "increase-decrease" texture changes during kohlrabi pickling process

Pickled kohlrabi is a traditional and favored vegetable product in China. During pickling, the hardness, springiness, and chewiness of kohlrabi all experienced a typical change with twice "increase-decrease" trend. However, little is known about its mechanism. In this study, in situ analysis including immunofluorescence, low field nuclear magnetic, and transmission electron microscopy were used to explore the effects of cell wall pectin, water state, and cellular structure on kohlrabi texture changes during pickling. Results revealed that at the early stage, due to the rapid loss of water after three times salting, the cells shrank and the interstitial space reduced, resulting in the first increase on kohlrabi texture. Subsequently, the dehydration-rehydration caused by the first brine processing resulted in the first decrease on kohlrabi texture. Then under the action of PME enzyme, more low-esterified pectin was produced, and chelate-soluble pectin with more branched structure was further formed, leading to another elevation of the sample texture. As the pickling continued, under the combined action of PG and PME, the molecular weight of pectin was decreased and the rigidity of the cell tissue was destroyed, caused kohlrabi texture continued to decline. These researches could provide important information and guidance for better maintaining the texture of pickled vegetables during processing.

Chemometric Comparison and Classification of 22 Apple Genotypes Based on Texture Analysis and Physico-Chemical Quality Attributes

The large number of cultivars belonging to the cultivated apple (Malus × domestica Borkh.) reflects an extremely wide range of variability, including for fruit quality traits. To evaluate some characteristics of fruit quality, 22 apple genotypes were selected from a collection of germplasms containing more than 600 accessions, based on different considerations, including the use of fruits (dessert, cooking, processing, juice, cider, multipurpose). The mean water content of the studied apple genotypes was 85.05%, with a coefficient of variation (CV) of 2.74%; the mean ash content was 2.32% with a CV of 22.1%, and the mean total soluble solids was 16.22% with a CV of 17.78%, indicating a relatively small difference between genotypes for these indices. On the contrary, relatively large differences were registered between genotypes for fruit weight, volume, and titratable acidity with means of 119.52 g, 155 mL, and 0.55% malic acid, and CVs of 35.17%, 34.58%, and 54.3%, respectively. The results showed that peel hardness varied between 3.80 and 13.69 N, the toughness between 0.2 and 1.07 mm, the flesh hardness between 0.97 and 4.76 N, and the hardness work between 6.88 and 27.84 mJ. The current study can emphasize the possibility of choosing the appropriate apple cultivars to cross in the breeding process and how future strategies can help apple breeders select breeding parents, which are essential key steps when breeding new apple cultivars. In addition, multivariate analysis has proven to be a useful tool in assessing the relationships between Malus genetic resources.