Investigation of blueberry juice fermentation by mixed probiotic strains: Regression modeling, machine learning optimization and comparison with fermentation by single strain in the phenolic and volatile profiles
Graphical abstract
Introduction
Probiotic fermented fruit and vegetable (F&V) juice, recognized as a nutritive product, is gaining more public concern and acceptability. Probiotics are defined as “Live microorganisms which when administered in adequate amounts confer a health benefit on the host” (FAO, 2006). The lactic acid bacterium is an important member of probiotics that have already been widely applied in the food industry. Probiotic fermentation has a profound influence on food composition. Briefly, proteases of lactic acid bacteria can decompose the corresponding substrates into free amino acids, improving the freshness of fermented products (Ren, & Li, 2022). Also, lactic acid bacteria can produce alcohols, esters, and other aromatic components to intensify the mellow fruit aroma (Li et al., 2018). Moreover, the complicated derivation reactions among polyphenols occur in the presence of lactic acid bacteria, improving the F&V juice taste and nutritional value (Sevindik et al., 2022). Many other benefits also exist with the probiotic fermentation of F&V juices, not limiting to the list aspects.
Lactic acid bacteria are widely distributed in the environments, and the microbial properties vary with the host materials. The typical food-grade lactic acid bacteria include Lactobacillus plantarum (Liu, Shao, Zhang, & Kang, 2020), Lactobacillus fermentum, Streptococcus thermophilus and others (Szutowska, 2020). In the microbial community, among different microbial species, there might be interactions if the microorganisms grow in the same environment, i.e. symbiosis and antagonism. Although most researches on mixed fermentation of F&V juices focus on fruit wine, increasing evidence reveals that the mixed fermentation of Saccharomyces cerevisiae, non-Saccharomyces yeasts and non-yeast strains can improve the wine quality substantially. For example, the volatile flavoring substances such as ethyl ester and fatty acids in white wine were enriched by the mixed fermentation of Pichia fermentans and S. cerevisiae (Ma, Yan, Wang, Zhang, & Tao, 2017). Also, the contents of anthocyanins and tannins in red wine were increased by the simultaneous fermentation of P. fermentans and S. cerevisiae (Kong et al., 2019). Besides, the mixed fermentation of bergamot juice by three types of Lactobacillus plantarum possessed stronger antioxidant capacity than the juices fermented by each species separately (Hashemi & Jafarpour, 2020). However, detailed studies about the F&V juice fermentation by various microbial strains are still scarce and need to be explored.
On the other hand, many F&V juices feature a low pH and high amount of soluble fiber and bioactive substances, i.e. polyphenols. This environment is adverse to the growth and metabolism of lactic acid bacteria. Several autochthonous L. fermentum and L. plantarum were isolated from different F&V in our previous work, some of which were potent in the bio-transformation of polyphenols in blueberry juices (Li, Tao et al., 2021). Meanwhile, in another study, we found that the fermentation of S. thermophilus improved the nutritional and sensory quality of blackberry and blueberry juices (Wu et al., 2021). Thus, it is important to examine the properties of the combination of these lactic acid bacterial species for the fermentation of F&V juices.
In recent years, mathematical tools, particularly experimental design and marchine learning algorithms, have been continuously applied in food science research. For instance, the combined mixture design (i.e. simplex lattice mixture design, simplex centroid design) and polynomial regression have been utilized to study the problems of food formulas (Rad, Pirouzian, Toker, & Konar, 2019). Meanwhile, the model optimization by genetic algorithm (GA) has been employed to accurately find the best solution to food problems, such as extraction, formula establishment, etc. (Tao et al., 2017). These methodologies can be considered when studying blueberry fermentation by mixed strains.
In this investigation, three previously studied probiotics (L. fermentum, L. plantarum and S. thermophilus) were selected as mixed fermentation cultures to ferment blueberry juice. The influence of mixed fermentation on the lactic acid accumulation and polyphenols enrichment were explored and optimized by the sequential simplex lattice mixture design, polynomial regression and GA optimization. Then, metabonomic data about phenolics, organic acids, and volatiles from mixed fermentation were compared with individual fermentation.
Section snippets
Materials
The blueberries with the variety Rabbiteye (Vaccinium ashei Reade) were provided by the blueberry plantation of JAAS (Jiangsu Academy of Agricultural Sciences) in Lishui District, Nanjing City in June 2019. After reaching the laboratory, the blueberries were stored in a freezer at −20 °C in the dark. The microbial strains L. plantarum LSJ-TY-HYB-T7 (CGMCC NO. 20596) and L. fermentum LSJ-TY-HYB-L16 (CGMCC NO. 20595) were isolated from cherry tomato and blueberry, respectively, which were
Influence of inoculation proportion on the fermentation characteristics of blue-berry juice
Following the simplex lattice mixture design, the experimentally detected responses after fermentation for 48 h are shown in Table 1 (lactic acid content and increment of total phenolic content) and Supplementary Table 1 (total anthocyanin content, viable cell count and pH). Generally, at the end of fermentation, the lactic acid content, increment of total phenolic content, total anthocyanin content, viable cell count and pH ranged from 2.839 to 3.468 g/L, 44.06–82.19 %, 116.90–229.46 mg
Conclusions
This study manifested obvious differences in the microbial metabolisms of organic acids, phenolics and volatiles among the fermentation of blueberry juices by individual lactic acid bacteria and their combination. The modeling and optimization results show that the combination of S. thermophilus with L. fermentum or L. plantarum failed to increase the total phenolic content in blueberry juices. Instead, L. fermentum and L. plantarum exhibit the synergetic effect of enriching the phenolic
CRediT authorship contribution statement
Weihua Liao: Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft. Juan Shen: Formal analysis, Investigation. Sivakumar Manickam: Writing – review & editing. Sujin Li: Formal analysis, Investigation. Yang Tao: Conceptualization, Methodology, Validation, Project administration, Resources, Supervision, Writing – review & editing. Dandan Li: Writing – review & editing. Dongfeng Liu: Resources. Yongbin Han: Project administration,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Fundamental Research Funds for the Central Universities, China (No. KYCXJC2022001), the National Natural Science Foundation of China (No. 32072351), Jiangsu Agricultural Science and Technology Independent Innovation Fund (No. CX(22)2026 and CX(21)3185) and Science and Technology Support Program of Jiangsu Province (No. BE2021353).
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