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In the present study, the incubation conditions of goat milk fermented by Lactobacillus bulgaricus LB6 were optimized to increase the angiotensin converting enzyme (ACE, EC 3.4.15.1) inhibitory activity by Box–Behnken design of response surface methodology. Incubation temperature, whey powder, and calcium lactate had significant effects on ACE inhibition rate and viable counts of LB6 during incubation. The results showed that optimal conditions of fermentation were found to be 37.05 °C, 0.8% (w/w) whey powder and 0.50% (w/w) calcium lactate. ACE inhibition rate increased significantly from 71.04 ± 0.37% to 83.31 ± 0.45% and the viable counts of Lactobacillus bulgaricus LB6 reached to 8.03 × 107 cfu·mL−1 under the optimal conditions, which approached the predicted values 83.25% and 8.04 × 107 cfu·mL−1. The optimal fermentation conditions can be a good reference for preparing ACE inhibitory peptides from goat milk.

Angiotensin I-converting enzyme (ACE) peptides are bioactive peptides that have important value in terms of research and application in the prevention and treatment of hypertension. While widespread literature is concentrated on casein or whey protein for production of ACE-inhibitory peptides, relatively little information is available on selecting the proper proteases to hydrolyze the protein. In this study, skimmed cow and goat milk were hydrolyzed by four commercial proteases, including alkaline protease, trypsin, bromelain, and papain. Angiotensin I-converting enzyme-inhibitory peptides and degree of hydrolysis (DH) of hydrolysates were measured. Moreover, we compared the difference in ACE-inhibitory activity between cow and goat milk. The results indicated that the DH increased with the increase in hydrolysis time. The alkaline protease-treated hydrolysates exhibited the highest DH value and ACE-inhibitory activity. Additionally, the ACE-inhibitory activity of hydrolysates from goat milk was higher than that of cow milk-derived hydrolysates. Therefore, goat milk is a good source to obtain bioactive peptides with ACE-inhibitory activity, as compared with cow milk. A proper enzyme to produce ACE-inhibitory peptides is important for the development of functional milk products and will provide the theoretical basis for industrial production.

Selenium-rich probiotics have the dual role of selenium and probiotics, and show great development potential in dairy products. Using Lacticaseibacillus rhamnosus L20 as the experimental strain, the effects of sodium selenite concentration and fermentation time on the growth and selenium conversion rate of L. rhamnosus L20, as well as the effects of carbon and nitrogen sources, prebiotics and inorganic salts on its growth were studied. The results showed that the appropriate sodium selenite concentration and fermentation time were 20 μg/mL and 16 h, and its selenium conversion rate and viable count were 88.83% and 2.34×108 CFU/mL, respectively. Carbon sources (glucose and lactose), organic nitrogen sources (soy peptone and beef extract), inorganic nitrogen sources (urea and Triammonium citrate), prebiotics (galactooligosaccharides and inulin) and inorganic salts (dipotassium hydrogen phosphate and sodium acetate) were beneficial to the growth of L. rhamnosus L20, and its dry weight was greater than 1.95 g/L, which provides a reference for further optimization of the proliferation culture medium of L. rhamnosus L20.

The development of probiotic products has attracted more and more attention. Products made from goat milk powder and probiotics can combine nutrition and health care functions. In this paper, the effects of different sugars, alcohols and antioxidants on the preparation goat milk tablets containing Bifidobacterium bifidum BB01 were studied by single factor experiment. The results showed that the appropriate addition of sugars, alcohols and antioxidants were as follows: sucrose 5 %, glucose 1.5 %, xylitol 3 %, ascorbic acid 0.03 %, D-sodium ascorbate 0.09 %, sodium ascorbate 0.03 %, microcrystalline cellulose 0.5 %, D-mannitol 0.1 %. According to the formulation, goat milk tablets with high Bifidobacterium activity were developed, and had appropriate hardness, friability and good sensory quality.

Cell envelope proteases (CEPs) can break down milk protein into peptides with different functions, which are of great benefit to human health. Therefore, the high-yield CEPs of Lactobacillus plantarum have the potential to produce functional dairy products. In previous experiments, we found that Na2HPO4, inulin, casein peptone and leucine have significant effects on CEP production by Lactobacillus plantarum LP69. So we proceeded to optimize the composition of the CEP-producing culture medium of L. plantarum through Box-Behnken design and response surface methodology. The protease activity, protein content and specific activity of CEPs produced by L. plantarum by inulin (0.2, 0.3, 0.4 %), casein peptone (0.4, 0.6, 0.8 %), Na2HPO4 (0.50, 0.52, 0.54 %) and leucine (14, 16, 18 mg/L) were evaluated. The optimal ratio of medium is 0.4 % inulin, 0.66 % casein peptone, 0.5 % Na2HPO4 and 14.04 mg/L Leucine. The final enzyme activity reached (24.46±0.81) U/mL, and the specific activity reached (1.41±0.46) U/mg.

Probiotics have many benefits for human intestinal health. However, Probiotics have poor tolerance to gastric acid and bile salts of the stomach. Microencapsulation could confer protection to probiotic against harsh environments effectively. In this experiment, Lactobacillus casei L61 was embedded by extrusion with gellan gum and chitosan as wall material. The viable cells and encapsulation yield of microcapsules were used as the indexes, the optimum values of each factor were determined by a single factor experiment. Chitosan concentration 0.50%, chitosan pH 4.5, gellan gum concentration 1.50%, the volume ratio of bacterial suspension to gellan gum is 1:6, the volume ratio of bacterial gum to chitosan is 1:4, the stirring time is 40min.

Angiotensin I converting enzyme (ACE) inhibitory peptides derived from milk proteins have obvious effect of lowering blood pressure, safe and non-toxic side effects. This study compared four commercial proteases, namely alcalase, flavourzyme, neutral protease and proteinase K for their ACE inhibitory activity in skimmed goat and cow milk and identified the best one with higher ACE inhibitory activity. The degree of hydrolysis (DH) of alcalase and proteinase K were much higher than flavourzyme, neutral protease for both skimmed goat and cow milk. Alcalase was the best enzyme to produce ACE inhibitory peptides from goat milk, with the ACE inhibitory activity 95.31%, while proteinase K was the optimal protease for hydrolyzing cow milk, with 81.28% ACE inhibitory activity. Furthermore, no correlation was obtained between the ACE inhibitory activity and DH for both goat and cow milk.

In order to improve the survival rate of probiotics and produce probiotic goat milk from fermented goat milk of Lactobacillus casei L61 by spray drying. Spray drying has been applied to large-scale industrial production of milk powder due to its high efficiency and low cost. However, high temperatures in spray drying can result in the loss of large numbers of probiotic.The purpose of this paper is to study the effects of eight thermal protectants including skim milk, sucrose, glucose, β-cyclodextrin, gelatin, maltodextrin, glycerol, trehalose on the survival rate and viable counts of L.casei L61 after heat treatment by the single factor experiment. All protective agents have a positive effect on increasing the survival rate of L.casei L61 (p<0.05). The results indicated that the survival rates of L.casei L61 were up to the maximum of 10.94%, 1.13%, 3.04%, 0.21%, 6.97%, 0.075, 4.71% and 0.29%, while the additions of skim milk, sucrose, glucose, β-cyclodextrin, gelatin, maltodextrin, glycerol, trehalose were 20mg/L, 10%, 7%, 15%, 1.5%, 3%, 8mL/L, 10%, respectively; the viable counts after heat treatment are 19.69, 0.81, 1.78, 0.455, 12.2, 0.12, 2.75, 0.435(×106CFU/mL), respectively. This paper provides technical a reference for the development of probiotic goat milk powder.

Exopolysaccharides (EPS) is a type of polysaccharide produced by lactic acid bacteria (LAB) that can be directly used in foods to make the products more excellent. Therefore, batch studies were performed to explore the effect of different LAB on the production of EPS and antioxidant activity. Five strains with high EPS yield and antioxidant activity were screened out from 66 strains isolated from Tibetan dairy products. The results show that EPS produntion of the five strains (B55, B62, B30, 7830 and K2) were 110.66, 145.48, 132.78, 122.11 and 111.72 mg·L−1, respectively, and they have a higher DPPH free radical scavenging activity (56.29, 66.43, 62.94, 68.71, 61.87%). Five LAB strains were identified and classified based on screening, purification and 16S rDNA sequences. Molecular characterization based on partial sequence 16S rDNA homology confirmed the initial identification as Lactobacillus fermentum (B55, B62), Lactobacillus plantarum (7830), Pediococcus acidilactici (B30) and Lactobacillus helveticus (K2).

Antioxidant peptides are currently the focus of many studies, since they eliminate free radicals in the human body without harmful effects. In the present study, Lactobacillus casei L61 was used as a starter culture to ferment goat milk because of its high capacity to produce antioxidant peptides. An optimal nutrients formula (casein, casein peptone, glucose, soybean peptone, inulin, calcium lactate, and cysteine) was investigated by Plackett–Burman (P–B) and Box–Behnken (B–B) designs for response surface methodology (RSM). Antioxidant peptides were successively isolated and purified from the fermented goat milk. Furthermore, the stability of the antioxidant peptides was evaluated in a simulated gastrointestinal tract at 37 °C. The results showed that calcium lactate, glucose, and casein peptone significantly affected the antioxidant activity of goat milk. The optimal additive amounts were 0.99% (w/v) calcium lactate, 0.21% (w/v) glucose, and 0.29% (w/v) casein peptone. The hydroxyl free radical scavenging rate increased significantly (p < 0.001) from 56.50 ± 0.57% to 88.01 ± 0.69%; the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging rate increased up to 63.48 ± 1.22% under the optimal conditions (n = 3). Our research provides a fitted mathematical model for antioxidant peptides production. Besides, these antioxidant peptides had great stability during simulated gastrointestinal digestion.