Mild heat stress limited the post-acidification caused by Lactobacillus rhamnosus hsryfm 1301 in fermented milk

The Effects of Compound Starter Culture, Sugar, and Soy Milk on the Quality and Probiotic Activity of Milk-Soy Mixed Yogurt

BACKGROUND

Yogurt has emerged as an essential nutritional food in contemporary diets, and the development of new multi-component yogurt formulations has become a focal point of current research.

OBJECTIVE

In this study, the effects of fermentation compounds and the addition of sugar and soy milk on the quality and probiotic activity of milk-soy mixed yogurt were studied to determine the optimal formation of mixed yogurt.

METHODS

The various fermentation compounds (YO-MIX 883, Lactobacillus casei complex starter cultures, and L. paracasei compound starter cultures), different concentrations of milk-soy additions (0, 25, 50, 75, and 100%) and sugar (2, 4, 6, and 8%) were tested within each experimental group, and the pH, appropriate acidity, and total viable bacterial count of the fermented milk-soy mixed yogurt were determined throughout the fermentation and refrigeration processes.

RESULTS

The obtained results showed that the L. paracasei complex was particularly effective for the fermentation of soy milk. The mixed yogurt formulation, comprising 50% soy milk and 4∼6% sucrose, exhibited enhanced acidity, superior sensory evaluation scores, and overall improved product quality. It was observed that during refrigeration an increase in the milk content of yogurt corresponded to a more pronounced post-acidification effect. The optimal formulation for the milk-soy mixed yogurt identified in this research consisted of 0.3% L. paracasei compound fermenter, 6% sucrose, and 40% soy milk. Under these optimal conditions, the mixed yogurt achieved an acidity level of 76°T, a sensory score of 92 points, and a survival index of 1.25. Additionally, the yogurt exhibited a distinctive soybean aroma in its aftertaste, contributing to its overall quality. Furthermore, the probiotic survival index of the mixed yogurt containing 40% soy milk, following simulated gastrointestinal fluid digestion, was recorded at 0.767, indicating that the probiotic activity in this yogurt was significantly higher than that of other yogurts.

CONCLUSION

The obtained results provide a theoretical foundation for the future industrial production of milk-soy mixed yogurt products.

HIGHLIGHTS

The mixed yogurt formulation, comprising 50% soy milk and 4∼6% sucrose, exhibited overall improved product quality. L. paracasei complex was more suitable for the fermentation of soy milk. Sucrose was more suitable for the fermentation of mixed yogurt. The more milk was added, the stronger the post-acidification effect of yogurt during refrigeration. The milk-soy mixed yogurt with high probiotic activity following artificial simulation of gastrointestinal fluid digestion had the potential for industrial production.

Pre-exposure of Lactobacillus acidophilus to stress conditions impacts the metabolites and bioaccessibility of calcium and carotenoids in fermented dairy products

This study evaluated the impact of fermentation with Lactobacillus acidophilus pre-subjected to acid, osmotic, and oxidative stress conditions on the production of metabolites and the bioaccessibility of nutrients and bioactive compounds in fermented milks and yogurts. The products were added with orange bagasse (additional calcium - Ca source) and buriti pulp (carotenoids source). Gas chromatography coupled with mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) were used to analyze the volatile and non-volatile compounds metabolites from fermentation, respectively. In vitro digestion assays (dialysis and micellization) evaluated the bioaccessibility of Ca and carotenoids. Results showed that fermentation with L. acidophilus, previously exposed to acid, osmotic, and oxidative stress conditions, increased the production of volatiles such as higher alcohols and compounds derived from amino acid catabolism (1-butanol, 1-decanol, 1-nonanol, nonanoic acid, 2-ethyl 1-hexanol, 1-methoxy-2-propanol). Also, when this microorganism was subjected to osmotic and oxidative stress, an increase in the bioaccessibility of Ca in natural fermented milks from 4.1 % to 13.3-15.5 % and in the same products fortified with orange bagasse from 5.3 % to 9.3-10.8 % (when compared to the non-stressed condition) were observed. Conversely, the use of L. acidophilus - non-stressed or subjected to oxidative stress - reduced the bioaccessibility of carotenoids in products containing buriti pulp from 9.6 % to 7.8 % and 4.1  % (in yogurts); and, from 4.1 % to 2.0 % (in fermented milks), when compared to control. Thus, the pre-exposure of probiotics to stress conditions may impact not only the sensory and biochemical characteristics of fermented products, but also the bioaccessibility of nutrients and bioactive compounds.

The Inoculation of Probiotics In Vivo Is a Challenge: Strategies to Improve Their Survival, to Avoid Unpleasant Changes, or to Enhance Their Performances in Beverages

The inoculation of probiotics in beverages (probiotication) requires special technologies, as probiotic microorganisms can experience stress during food processing (acid, cold, drying, starvation, oxidative, and osmotic stresses) and gastrointestinal transit. Survival to harsh conditions is an essential prerequisite for probiotic bacteria before reaching the target site where they can exert their health promoting effects, but several probiotics show a poor resistance to technological processes, limiting their use to a restricted number of food products. Therefore, this paper offers a short overview of the ways to improve bacterial resistance: by inducing a phenotypic modification (adaptation) or by surrounding bacteria through a physical protection (microencapsulation). A second topic briefly addressed is genetic manipulation, while the last section addresses the control of metabolism by attenuation through physical treatments to design new kinds of food.