Tibetan Plateau yak milk: A comprehensive review of nutritional values, health benefits, and processing technology

Yak milk is a characteristic animal product of yaks in the Qinghai-Tibet Plateau. Although yak milk production is low, it is richer in nutrients such as protein, fat, and lactose, a more comprehensive range of bioactive components, and unique microbial resources than Holstein cow milk. The plateau environment makes yak milk resistant to hypoxia, anti-fatigue, antioxidant, antibacterial, and relieves chronic diseases. In this paper, based on the systematic analysis of yak milk research results in the past 20 years using CiteSpace 6.1.R2, we reviewed yak lactation performance and nutritional efficacy of yak milk. This paper summarizes the improvement of traditional yak dairy processing technology, and also focuses on the microbial diversity of yak milk sources and their beneficial effects. The purpose of this review is to provide scientific support for the development of a quality yak milk industry on the Tibetan plateau.

Microbial Community and Fermentation Characteristics of Native Grass Prepared Without or With Isolated Lactic Acid Bacteria on the Mongolian Plateau

This study aimed to isolate and identify lactic acid bacteria (LAB) from the native grass and naturally fermented silage from the Mongolian Plateau. The effect of selected strains on bacterial community and quality of native grass silage was also studied. Strains XM2, 265, and 842 could grow normally at 15°C–30°C, pH 4.0–8.0, and NaCl 3 and 6.5%; they were identified as Lactiplantibacillus plantarum subsp. plantarum, Pediococcus acidilactici, and Latilactobacillus graminis, by sequencing 16S rRNA, respectively. The three strains (XM2, 265, and 842) and one commercial additive (L) were used as inoculants and singularly added to the native grass. Compared to the control, the dry matter content was significantly (p < 0.05) lower in L and XM2 groups. The water-soluble carbohydrate content was significantly (p < 0.05) higher in control than in other groups. Compared with the control, the crude protein and ammonia nitrogen contents were significantly (p < 0.05) higher and lower in the LAB-treated groups, and the acid and detergent fiber contents were significantly (p < 0.05) reduced in the L and XM2 groups than those in other groups. There was a significant (p < 0.05) difference in the pH value, lactic acid content, and lactic acid-to-acetic acid ratio in L and XM2 groups than in other groups. Compared with the control, the number of LAB was significantly (p < 0.05) higher in LAB-treated silages, whereas no significant (p > 0.05) differences were observed in yeast and aerobic bacteria in all groups. Compared to the control, the Shannon index was significantly (p < 0.05) reduced. Simpson and Chao1 were significantly (p < 0.05) increased. Principal coordinate analysis based on the unweighted UniFrac distance showed clear separation of the bacterial community in fresh materials and LAB-treated silages. Besides, compared to the control, the principal coordinate analysis of LAB-treated silages was also separate. After 30 days of fermentation, the relative abundance of Firmicutes increased and was the primary phylum in all silages. Compared with the control, the abundance of Firmicutes and Proteobacteriawas significantly (p < 0.05) higher and lower in L and XM2 groups. In contrast, no significant differences were observed among control, 265, and 842 groups. At the genus level, the relative abundance of Lactobacillus, Enterobacter, Pediococcus, and Weissella was increased and dominated the native grass fermentation. Compared with the control, the abundance of Lactobacillus was significantly (p < 0.05) higher in L, XM2, and 842 groups, while no significant (p > 0.05) differences were observed between the control and 265 groups. The abundance of Pediococcus was higher than that in other groups. Consequently, the results demonstrated that LAB significantly influenced silage fermentation by reconstructing microbiota, and Lactobacillus was the dominant genus in the native grass silages. Furthermore, the results showed that strain XM2 could effectively improve the silage quality, and it is considered a potential starter for the native grass silage.

Effects of different additives on fermentation quality and aerobic stability of a total mixed ration prepared with local feed resources on Tibetan plateau

To improve the utilization efficiency of total mixed ration (TMR) on Tibetan plateau, the effects of different additives on fermentation quality and aerobic stability of the ensiled TMR prepared with local feed resources were studied. A total of 150 experimental silos were prepared in a completely randomized design to evaluate the following treatments: (a) control; (b) Lactobacillus buchneri; (c) acetic acid; (d) propionic acid; (e) 1,2-propanediol; and (f) 1-propanol. After 90 days of ensiling, silos were opened for fermentation quality and in vitro parameters analysis, and then subjected to an aerobic stability test for 14 days. The acetic acid, 1,2-propanediol and 1-propanol treatments increased (p < .05) pH and acetic acid content, and lowered (p < .05) the lactic acid production in comparison to control. There were no statistically significant differences in in vitro digestibility parameters among the treatments. Treatments of acetic acid, 1,2-propanediol and 1-propanol substantially improved the aerobic stability of the ensiled TMR, as indicated by almost unchanged pH and lactic acid contents throughout the aerobic exposure test. These results indicated that acetic acid, 1,2-propanediol and 1-propanol had no adverse effect on in vitro digestibility and could be effective additives for enhancing the aerobic stability of ensiled TMR prepared on Tibetan plateau.

Characterization of Enterococcus hirae Isolated from the Intestine of Seabass (Lates Calcarifer) as a New Potential Probiotic against Pathogenic Vibrios

In this study, we aimed to isolate, identify and characterize lactic acid bacteria (LAB) from the intestine of juvenile seabass (Lates calcarifer) as a new potential probiotic. Four strains of LABs were isolated from the intestines of ten healthy seabass juveniles. In the in vitro screening process using spot lawn assay, one isolate labeled as LAB3 showed inhibitory activity against Vibrio harveyi (ATCC 35,084). Strain LAB3 was determined to belong to the gram positive bacteria group with cocci shape and was identified as Enterococcus hirae using 16S rDNA analysis. This bacterium was able to grow at pH ranging from pH 2 to 10 with the best growth at pH 7. This strain was also able to grow at 0-4% NaCl after 24 h incubation and grew best at 1.5% NaCl. Enterococcus hirae strain LAB3 of the present study is worthy to be further characterized as a potential probiotic for use in seabass culture.

Preparation, Bioavailability, and Mechanism of Emerging Activities of Ile-Pro-Pro and Val-Pro-Pro

Ile-Pro-Pro and Val-Pro-Pro are two most well-known food-derived bioactive peptides, initially identified as inhibitors of angiotensin I-converting enzyme (ACE) from a sample of sour milk. These two peptides were identified in fermented and enzymatic hydrolyzed cow and non-cow (that is, goat, sheep, buffalo, yak, camel, mare, and donkey) milk, as well as sourdough prepared from wheat, rye, and malt. Similar to other bioactive peptides, bioavailability of these peptides is low (about 0.1%), reaching picomolar concentration in human plasma; they showed blood pressure lowering activity in animals and in human, via improved endothelial function, activation of ACE2, and anti-inflammatory property. Emerging bioactivities of these two peptides toward against metabolic syndrome and bone-protection received limited attention, but may open up new applications of these peptides as functional food ingredients. Further studies are warranted to determine the best source as well as to identify novel enzymes (particularly from traditional fermented milk products) to improve the efficiency of production, to characterize possible peptide receptors using a combination of omics technology with molecular methods to understand if these two peptides act as signal-like molecules, to improve their bioavailability, and to explore new applications based on emerging bioactivities.

Assessment of the Antimicrobial Potentiality and Functionality of Lactobacillus plantarum Strains Isolated from the Conventional Inner Mongolian Fermented Cheese Against Foodborne Pathogens

Lactobacillus plantarum are amongst the diversified lactic acid bacteria (LAB) species which are being utilized abundantly in the food industry. Numerous L. plantarum strains have been reported to produce several antimicrobial compounds. Diacetyl, hydrogen peroxide, organic acids, as well as bacteriocins can also be exemplified by a variable spectrum of actions. The current study was intended to conduct the screening and characterization of antimicrobial prospective of L. plantarum from traditional Inner Mongolian fermented hard cheese. Foodborne pathogens, Salmonella typhimurium, Escherichia coli O157:H7, Listeria monocytogenes, and Staphylococcus aureus, were examined by using the Oxford cup technique and the mixed culture inhibition assays. The resulting analyses disclosed that L. plantarum KLDS1.0344 indicated broad antimicrobial spectrum against all selected pathogens as compared to other LAB used in this study. Additionally, the decrement of the pathogen population was observed up to 3.47 logs in mixed culture inhibition assays. L. plantarum KLDS 1.0344 acid production was recorded up to 71.8 ± 3.59 °D in mixed culture while antimicrobial particles released in cell free supernatants demonstrated bacteriocin-like characteristics showing substantial pH stability (2.0–6.0), proteolytic enzyme reduced the antibacterial activity (15.2 ± 0.6 mm–20.4 ± 0.8 mm), heat stability (20 min at 120 °C) against selected pathogens. Moreover, the spectrum range of antimicrobial peptides after the partial purification was decreased as compared to the crude bacteriocin-like compound. The SDS-PAGE analysis showed the molecular weight range of partially purified bacteriocin from 12 to 45 kDa. After analyzing the obtained data from the current experimentation showed that the capability of L. plantarum KLDS 1.0344 to oppose the pathogen growth in vitro relies on the occurrence of organic acids along with bacteriocin-like compounds proving L. plantarum KLDS 1.0344 as a potentially appropriate candidate as an alternative bio-control agent against foodborne pathogens.

Short communication: Enzymatic perspective of galactosidases reveals variations in lactose metabolism among Lactococcus lactis strains

To date, most studies of lactose utilization have focused on the genetic diversity of lactic acid bacteria or its influence on product quality, but phenotypic evaluation has rarely been based on metabolic characteristics. In the present study, we investigated the growth, acid production, β-galactosidase, and 6-phospho-β-galactosidase activities of 16 Lactococcus lactis strains obtained from various habitats with lactose as the sole carbon source. The 15 L. lactis strains obtained from various habitats exhibited significant differences in growth and acid production characteristics in the de Man, Rogosa, and Sharpe-lactose broth, and 4 strains consumed more lactose when cultured in skim milk than the type strain ATCC 19435. Among these strains, DQHXNQ38-12 mainly produced acetoin and diacetyl when cultured in skim milk, whereas the strains 15M2 and 5G2 produced high levels of acid and formed curd rapidly. We concluded that the use of lactose is necessary for strain adaptation to the dairy niche. Comprehensive studies of lactose use and the fermentation characteristics of L. lactis are of significant importance.

Phylogenetic identification of lactic acid bacteria isolates and their effects on the fermentation quality of sweet sorghum (Sorghum bicolor) silage

AIM

To isolate, screen and identify the lactic acid bacteria (LAB) from elephant silage during the process of the fermentation and their effects on the fermentation quality of sweet sorghum silage.

METHODS AND RESULTS

The isolated strains were identified based on morphological, physiological and biochemical characteristics as well as 16S rRNA analysis. Seven LAB strains were isolated from elephant grass silage. Three strains (Pediococcus acidilactici (AZZ1), Lactobacillus plantarum subsp. plantarum (AZZ4), L. plantarum subsp. argentoratensis (AZZ7) and one commercial bacteria L. plantarum, ecosyl MTD/1(CB)) were chosen as additives at 6 log colony forming units per gram of fresh sweet sorghum grass in laboratory silos (680 g). Silos for each treatment were opened after 5, 7, 14, 30 and 60 days, respectively. All isolates were characterized as Gram-positive, catalase-negative and grow normally in 6·5% NaCl. The strains AZZ1, AZZ2 and AZZ5, were identified as Pediococcus genus while AZZ3, AZZ4, AZZ6 and AZZ7 were Lactobacillus genus. Compared to the control, all the isolates improved the silage quality of sweet sorghum silage, indicated by significantly (P < 0·05) lower pH and ammonia-nitrogen contents and undesirable micro-organism counts, and higher lactic acid (LA) contents and ratios of lactic acid/acetic acid. During ensiling, AZZ4 performed better among all of inoculants, indicated by significantly (P < 0·05) decreased on pH and ammonia-N contents and higher increased on LA contents.

CONCLUSION

Strain AZZ4 is recommended as starter culture for sweet sorghum.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first time to investigate the effects of LAB isolates from elephant grass silage and use them as additives, which is to find out how LAB inoculants improve the fermentation quality of sweet sorghum silage.

Bacterial diversity and community in Qula from the Qinghai-Tibetan Plateau in China

Qula is a cheese-like product usually prepared with unpasteurized yak milk under open conditions, with both endogenous and exogenous microorganisms involved in the fermentation process. In the present study, 15 Qula samples were collected from five different regions in China to investigate the diversity of microbial communities using high-throughput sequencing targeting the V3–V4 region of 16S rRNA gene. The bacterial diversity significantly differed among samples of different origins, indicating a possible effect of geography. The result also showed that microbial communities significantly differed in samples of different origin and these differences were greater at the genus than the phylum level. A total of six phyla were identified in the samples, and Firmicutes and Proteobacteria had a relative abundance >20%. A total of 73 bacterial genera were identified in the samples. Two dominant genera (Lactobacillus and Acetobacter) were common to all samples, and a total of 47 operational taxonomic units at different levels significantly differed between samples of different origin. The predicted functional genes of the bacteria present in samples also indicated differences in bacterial communities between the samples of different origin. The network analysis showed that microbial interactions between bacterial communities in Qula were very complex. This study lays a foundation for further investigations into its food ecology.

Characteristics of Pediococcus pentosaceus Q6 isolated from Elymus nutans growing on the Tibetan Plateau and its application for silage preparation at low temperature

AIMS

Characteristics of a strain Pediococcus pentosaceus Q6 isolated from Elymus nutans growing on the Tibetan plateau and its effects on E. nutans silage fermentation stored at low temperature were investigated.

METHODS AND RESULTS

Sugar fermentation pattern and growth profiles of the strain Q6 and its reference strain APP were characterized. The strain Q6 and APP were inoculated to E. nutans at ensiling respectively; and ensiled at different temperatures (10, 15 and 25°C) for 30, 60 and 90 days. The results indicated that Q6 could grow at pH 3·0 and at 4°C. In contrast to APP, Q6 could ferment mannitol, saccharose, sorbitol and rhamnose. Lower pH in Q6-treated silages fermented for 60 days at 10 and 15°C was found compared with the control and APP-treated groups. For the silages that were stored at 10 or 15°C, the greatest lactic acid content were detected in Q6-inoculated silages ensiled for 30 and 60 days respectively. There were no differences in pH and lactic acid content between Q6- and APP-treated silages ensiled at 10 and 15°C for 90 days respectively.

CONCLUSIONS

Inoculation of the strain P. pentosaceus Q6 could improve fermentation quality of ensiled E. nutans at the early stage of ensiling stored at low temperature (10 or 15°C).

SIGNIFICANCE AND IMPACT OF THE STUDY

The selection of P. pentosaceus inoculants for improving silage quality at low temperature, which provides a candidate strain to make high-quality silage in regions with frigid climate.

Screening and investigation Lactobacillius spp. to improve Secale cereale silage quality

Silage is a high-moisture-content forage that is used to feed livestock. Using silage as feed is economically feasible and suitable for cattle management. Secale cereale is considered as a high-quality forage plant. After the heading stage the biomass of S. cereale increases by up to 30%; however, lignification in the cell wall causes low fermentation efficiency and coefficient digestibility, and it may also be contaminated by mycotoxin-producing fungi and can impair the quality of the silage. Therefore, the aim of this study was to screen beneficial Lactobacillius spp. for S. cereale silage to reduce fungi contamination and to increase fibrinolytic ability in the silage. Up to 100 days fermentation period and total 180 lactic acid bacteria were isolated and only a single isolate, R4-26, showed strong acidification ability and antifungal activities against mycotoxin-producing fungus. According to quantitative RT-PCR results, the mycotoxin-producing fungal contamination was significantly reduced in the S. cereale silage containing the R4-26 isolate. In enzymatic assays, only a single isolate, R48-27 demonstrated cellulase, xylanase, chitinase and esterase activities. In conclusion, the beneficial Lactobacillius spp. strains have the ability to reduce mycotoxigenic fungi contamination and increase fibrinolytic activity to improve quality of the S. cereale silage.

Characteristics of lactic acid bacteria isolates and their effect on the fermentation quality of Napier grass silage at three high temperatures

BACKGROUND

The poor fermentation quality of silage is an important issue for silage production during the high temperatures of summer. Pediococcus acidilactici GG13 (GG13) and Lactobacillus rhamnosus GG26 (GG26) isolated from Italian ryegrass (Lolium multiflorum Lam.) silage were characterised by morphological and physiological tests and 16S rRNA sequencing analysis, and their effects, along with those of a commercial lactic acid bacteria (LAB) inoculant (CB), on the fermentation quality of facultative halophyte Napier grass (Pennisetum purpureum Schumach) ensiled at 30 °C, 40 °C and 50 °C were studied, respectively.

RESULT

The strains GG13 and GG26 grew well at 50 °C and pH 3.5, and were tolerant to 6.5% NaCl. After ensiling for 50 days, the strains GG13 and GG26 and the CB decreased (P < 0.001) the pH and acetic acid and ammonia-N contents and increased (P < 0.001) the lactic acid contents at 30 °C, and decreased (P < 0.001) the ammonia-N contents at 40 °C in Napier grass. CB did not affect the fermentation quality at 50 °C, whereas both isolated strains improved the fermentation quality of Napier grass silage as indicated by the lower (P < 0.001) pH, butyric acid and ammonia-N contents and higher (P < 0.001) lactic acid contents. The strain GG13 is better than GG26 with regard to improvement in fermentation quality of Napier grass silage.

CONCLUSIONS

The results of this study suggested that strain GG13 is a good LAB inoculant for producing well-fermented silages during the high temperatures of summer times. © 2016 Society of Chemical Industry.

Study on Streptococcus thermophilus isolated from Qula and associated characteristic of acetaldehyde and diacetyl in their fermented milk

In this study, the lactic acid bacterial population of Qula cheese from the Gansu and Sichuan provinces of China were isolated and identified. Eight strains of Streptococcus thermophilus were isolated, of which five strains were selected for further characterization based on their fermentation properties. The changes in a number of parameters, including titration acidity, pH, viable counts, PrtS protease activity and the production of acetaldehyde, diacetyl and organic acid, were monitored during fermentation and the storage of fermented milks produced by the respective strain. All of the strains displaying acidifying capacity and all five fermented milks maintained high viable counts of S. thermophilus from fermentation to storage. Our study found that the changes in the monitored parameters were strain-specific and varied considerably among the five tested strains. Fermented milks produced by strain IMAU80809 had the highest concentration of acetaldehyde and were most favorable in the sensory evaluation. This study confirms that Qula cheese is a good source for isolating novel lactic acid bacterial strains with different fermentation properties, which will be very useful for further development and industrialization of traditionally fermented dairy products.

The effects of replacement of whole-plant corn with oat and common vetch on the fermentation quality, chemical composition and aerobic stability of total mixed ration silage in Tibet

The objective of this experiment was to evaluate the effects of replacement of whole-plant corn with oat and common vetch on the fermentation quality, chemical composition and aerobic stability of total mixed ration (TMR) silage in Tibet. Four TMR that varied in the forage sources on dry matter basis were used: (i) 52% whole-plant corn (Control); (ii) 43% oat + 12% common vetch (OC3.6); (iii) 38% oat + 18% common vetch (OC2.2); and (iv) 33% oat + 23% common vetch (OC1.5). Silos were opened on day 45 and then subjected to an aerobic stability test for 12 days. The results showed that all silages were well preserved with low pH and NH3 -N, and high lactic acid and V-scores. With the increasing proportion of common vetch, crude protein, ether extract increased (P < 0.05), and neutral detergent fiber and acid detergent fiber decreased (P < 0.05). Under aerobic conditions, treated silages were more stable than the control silage as indicated by lower (P < 0.05) pH and yeast population. It was concluded that replacement of whole-plant corn with oat and common vetch had no unfavorable effects on the fermentation quality and improved crude protein content and aerobic stability of TMR silage. OC2.2 silage was the best among three treated TMR silages.

Effect of Applying Molasses and Propionic Acid on Fermentation Quality and Aerobic Stability of Total Mixed Ration Silage Prepared with Whole-plant Corn in Tibet

The objective of this study was to evaluate the effects of molasses and propionic acid on the fermentation quality and aerobic stability of total mixed ration (TMR) silages prepared with whole-plant corn in Tibet. TMR (354 g/kg DM) was ensiled with four different treatments: no additive (control), molasses (M), propionic acid (P), and molasses+propionic acid (PM), in laboratory silos (250 mL) and fermented for 45 d. Silos were opened and silages were subjected to an aerobic stability test for 12 days, in which chemical and microbiological parameters of TMR silages were measured to determined the aerobic deterioration. After 45 d of ensiling, the four TMR silages were of good quality with low pH value and ammonia/total N (AN), and high lactic acid (LA) content and V-scores. M silage showed the highest (p<0.05) LA content and higher dry matter (DM) recovery than the control and P silages. P silage had lower (p<0.05) LA content than the control silage. During aerobic exposure, lactic acid contents decreased gradually in the control and M silages, while that of P and PM silages increased, and the peak values were observed after 9 d. M silage had similar yeast counts with the control silage (>10(5) cfu/g FM), however, it appeared to be more stable as indicated by a delayed pH value increase. P and PM silages showed fewer yeasts (<10(5) cfu/g FM) (p<0.05) and were more stable than the control and M silages during aerobic exposure. It was concluded that M application increased LA content and improved aerobic stability of TMR silage prepared with whole-plant corn in Tibet. P application inhibited lactic acid production during ensiling, and apparently preserved available sugars which stimulated large increases in lactic acid during aerobic exposure stage, which resulted in greater aerobic stability of TMR silage.

Naturally occurring lactic Acid bacteria isolated from tomato pomace silage

Silage making has become a significant method of forage conservation worldwide. To determine how tomato pomace (TP) may be used effectively as animal feed, it was ensilaged for 90 days and microbiology counts, fermentation characteristics and chemical composition of tomato pomace silage (TPS) were evaluated at the 30th, 60th, and 90th days, respectively. In addition, 103 lactic acid bacteria were isolated from TPS. Based on the phenotypic and chemotaxonomic characteristics, 16S rDNA sequence and carbohydrate fermentation tests, the isolates were identified as 17 species namely: Lactobacillus coryniformis subsp. torquens (0.97%), Lactobacillus pontis (0.97%), Lactobacillus hilgardii (0.97%), Lactobacillus pantheris (0.97%), Lactobacillus amylovorus (1.9%), Lactobacillus panis (1.9%), Lactobacillus vaginalis (1.9%), Lactobacillus rapi (1.9%), Lactobacillus buchneri (2.9%), Lactobacillus parafarraginis (2.9%), Lactobacillus helveticus (3.9%), Lactobacillus camelliae (3.9%), Lactobacillus fermentum (5.8%), Lactobacillus manihotivorans (6.8%), Lactobacillus plantarum (10.7%), Lactobacillus harbinensis (16.5%) and Lactobacillus paracasei subsp. paracasei (35.0%). This study has shown that TP can be well preserved for 90 days by ensilaging and that TPS is not only rich in essential nutrients, but that physiological and biochemical properties of the isolates could provide a platform for future design of lactic acid bacteria (LAB) inoculants aimed at improving the fermentation quality of silage.

Improvement of Fermentation and Nutritive Quality of Straw-grass Silage by Inclusion of Wet Hulless-barley Distillers' Grains in Tibet

In order to develop methods that would enlarge the feed resources in Tibet, mixtures of hulless-barley straw and tall fescue were ensiled with four levels (0, 10%, 20%, and 30% of fresh weight) of wet hulless-barley distillers’ grains (WHDG). The silos were opened after 7, 14 or 30 d of ensiling, and the fermentation characteristics and nutritive quality of the silages were analyzed. WHDG addition significantly improved fermentation quality, as indicated by the faster decline of pH, rapid accumulation of lactic acid (LA) (p<0.05), and lower butyric acid content and ammonia-N/total N (p<0.05) as compared with the control. These results indicated that WHDG additions not only effectively inhibited the activity of aerobic bacteria, but also resulted in faster and greatly enhanced LA production and pH value decline, which restricted activity of undesirable bacteria, resulting in more residual water soluble carbohydrates (WSC) in the silages. The protein content of WHDG-containing silages were significantly higher (p<0.05) higher than that of the control. In conclusion, the addition of WHDG increased the fermentation and nutritive quality of straw-grass silage, and this effect was more marked when the inclusion rate of WHDG was greater than 20%.

Characteristics of lactic acid bacteria isolates and their inoculating effects on the silage fermentation at high temperature

Thermotolerant strains of lactic acid bacteria (LAB) were screened for their suitability for silage making at high temperatures. Four selected strains were identified by 16S rRNA sequencing analyses and added to unwilted and wilted Italian ryegrass for ensiling at 45°C. All four strains (HT1, HT2, HT3 and HT4) grew at 50°C and pH 4·0. Strains HT1 and HT2 were identified as Lactobacillus rhamnosus; HT3 and HT4 were identified as Lact. fermentum. Strains HT1 and HT2 were the most effective at improving the fermentation quality of Italian ryegrass silage, irrespective of wilting, as indicated by lower pH values, less NH(3) -N, and more lactic acid. In contrast, strains HT3, HT4 and a commercial inoculant consisting of Lact. plantarum and Pediococcus acidilactici conferred no or reduced benefits. Wilting alone did not improve the fermentation quality of Italian ryegrass at 45°C. Inoculating with thermotolerant Lact. rhamnosus HT1 and HT2 could improve the fermentation quality of silage at high temperatures. Lactobacillus rhamnosus HT1 and HT2 can be used as inoculants for silage making in the tropics and subtropics and could play an important role in developing silage production in such regions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Grasses are often difficult to ensile in the tropics and subtropics because of the high temperatures there. To solve this problem, we screened for thermotolerant lactic acid bacteria and obtained two valuable strains of Lactobacillus rhamnosus, HT1 and HT2, which proved to be beneficial to silage fermentation at high temperatures. Lactobacillus rhamnosus HT1 and HT2 can be used as inoculants for silage making in the tropics and subtropics, and will play an important role in developing silage production in such regions.

Characteristics of isolated lactic acid bacteria and their effectiveness to improve stylo (Stylosanthes guianensis Sw.) silage quality at various temperatures

Two lactic acid bacteria (LAB) strains, Pediococcus pentosaceus SC1 and Lactobacillus paraplantarum SC2 isolated from king grass silage, were characterized and their effectiveness to improve the silage fermentation quality of stylo (Stylosanthes guianensis Sw.) was studied. Strain SC1 was able to grow at a high temperature of 45°C, while SC2 did not. SC2 normally grew at a low pH of 4.0, while SC1 could not. These two strains and a commercial inoculant of LAB (L. plantarum, LP) were used as additives to stylo silage preparation at various temperatures (20°C, 30°C and 40°C). All LAB inoculants significantly (P < 0.05) reduced the pH value and ammonia-N content, and increased the ratio of lactic acid to acetic acid and quality score compared with the control. In addition, inoculating LAB strains markedly (P < 0.05) reduced butyric acid content at the temperatures of 30°C and 40°C. Compared to SC2 and LP strains, strain SC1 was the most effective for improving stylo silage quality at 20°C, indicated by the increase in lactic acid, ratio of lactic acid to acetic acid and quality score. At 30°C and 40°C, there were no significant differences among SC1, SC2 and LP treatments in pH values, contents of acetic acid, butyric acid and ammonia-N (P > 0.05).

Lactococcus fujiensis sp. nov., a lactic acid bacterium isolated from vegetable matter

Three strains of lactic acid bacteria, designated NJ 317T, NJ 414 and NJ 415, were isolated from the outer leaves of Chinese cabbages (Brassica rapa L. var. glabra Regel) and characterized taxonomically. The strains were Gram-reaction-positive, catalase-negative, facultatively anaerobic cocci that did not produce gas from glucose and formed l-lactic acid. The major fatty acids were C18 : 1ω9c, C16 : 0, C14 : 0 and summed feature 10. Morphological, physiological and phylogenetic data indicated that the strains belonged to the genus Lactococcus. These strains shared similar phenotypic characteristics and exhibited DNA relatedness values >96.6 % to each other, indicating that they represent a single species. The DNA G+C contents of the three strains were 42.1–42.5 mol%. 16S rRNA gene sequences of the novel strains were determined and aligned with those of other species of the genus Lactococcus. On the basis of phylogenetic analysis the three strains grouped with other members of the genus Lactococcus. Lactococcus lactis and Lactococcus garvieae were the most closely related species, sharing a sequence similarity value of 94.4 % with the three strains. Ribotyping patterns, however, revealed that these strains were well-separated from reference strains of species of the genus Lactococcus and DNA–DNA hybridization studies indicated that the novel strains had low levels (<20.2 %) of DNA relatedness with reference strains of L. lactis, L. garvieae and other type strains of previously described species, showing that they represent a different species. Based on this evidence, strains NJ 317T, NJ 414 and NJ 415 represent a novel species of the genus Lactococcus, for which the name Lactococcus fujiensis sp. nov. is proposed. The type strain is NJ 317T ( = JCM16395T  = CGMCC 1.10453T).

Novel multiplex polymerase chain reaction primer set for identification of Lactococcus species

AIMS

The gram-positive bacterial genus Lactococcus has been taxonomically classified into seven species (Lactococcus lactis, Lactococcus garvieae, Lactococcus piscium, Lactococcus plantarum, Lactococcus raffinolactis, Lactococcus chungangensis and Lactococcus fujiensis). This study aimed to develop a novel multiplex polymerase chain reaction (PCR) primer set for the identification of the seven lactococcal species, as well as to differentiate the two industrially important dairy subspecies, L. lactis subsp. lactis and L. lactis subsp. cremoris.

METHODS AND RESULTS

A multiplex PCR primer set was designed based on the nucleotide sequences of the 16S rRNA gene of the seven lactococcal species. The specificity of the established one-step multiplex PCR scheme was verified using more than 200 bacterial strains, in which a complete sequence match was confirmed by partial sequencing of their 16S rRNA gene.

CONCLUSIONS

The one-step multiplex PCR enables the identification and speciation of bacterial strains belonging to the genus Lactococcus and the differentiation of strains of L. lactis subsp. lactis and L. lactis subsp. cremoris.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work provides an efficient method for identification of lactococcal strains of industrial importance.

Natural populations of lactic acid bacteria isolated from vegetable residues and silage fermentation

Natural populations of lactic acid bacteria (LAB) and silage fermentation of vegetable residues were studied. Fifty-two strains of LAB isolated from cabbage, Chinese cabbage, and lettuce residues were identified and characterized. The LAB strains were gram-positive and catalase-negative bacteria, which were divided into 6 groups (A to F) according to morphological and biochemical characteristics. The strains in group A were rods that did not produce gas from glucose and formed the d and l isomers of lactate. Groups B and C were homofermentative cocci that formed l-lactic acid. Groups D, E, and F were heterofermentative cocci that formed d-lactic acid. Based on 16S rDNA gene sequence analysis, group A to F strains were identified as Lactobacillus plantarum, Lactococcus piscium, Lactococcus lactis, Leuconostoc citreum, Weissella soli and Leuconostoc gelidum, respectively. The prevalent LAB, predominantly homofermentative lactobacilli, consisted of Lactobacillus plantarum (34.6%), Weissella soli (19.2%), Leuconostoc gelidum (15.4%), Leuconostoc citreum (13.5%), Lactococcus lactis (9.6%), and Lactococcus piscium (7.7%). Lactobacillus plantarum was the dominant member of the LAB population in 3 types of vegetable residues. These vegetable residues contained a high level of crude protein (20.2 to 28.4% of dry matter). These silages prepared by using a small-scale fermentation system were well preserved, with low pH and a relatively high content of lactate. This study suggests that the vegetable residues contain abundant LAB species and nutrients, and that they could be well preserved by making silage, which is a potentially good vegetable protein source for livestock diets.

16S ribosomal DNA analysis and characterization of lactic acid bacteria associated with traditional Tibetan Qula cheese made from yak milk

Twenty strains of lactic acid bacteria were isolated from six traditional Tibetan Qula cheese made from yak which were collected from northwest China, including Tibet, Qinghai and Gansu province. These isolates were subjected to phenotypic and genetic analyses. All isolates were Gram-positive and catalase-negative cocci that produced gas from glucose and formed D(-) isomer of lactate. Most isolates were able to grow in de Man, Rogosa and Sharpe (MRS) broth at pH values 3.0-9.0 and in 6.5% NaCl (w/v). According to analytical profile index 50 carbohydrates (API 50 CH) fermentation patterns of amygdalin and arabinose, these isolates were divided into three groups (A to C). On the basis of the phylogenetic trees of 16S ribosomal DNA (rDNA) sequence, the strains in all groups were placed in the cluster making up the genus Leuconostoc, which showed that all strains should belong to Leuconostoc species. Strains in Group A and Group B exhibited similarity of 16S rDNA sequence of over 99% to Leuconostoc mesenteroides, indicating that they each comprised a single species. Strains in group C were assigned to the Leuconostoc pseudomesenteroides and their 16S rDNA sequence showed a similarity of over 99%. This study demonstrated that Leuconostoc was the dominant member among lactic acid bacteria in Qula cheese.

Rapid identification of lactic acid bacteria isolated from home-made fermented milk in Tibet

Fermented milk is a very delicious and nutritional food distributed in the international markets. Rapid preliminary identification of lactic acid bacteria to the species level is an important issue for the fermentation industry. One hundred seventy-one strains of lactic acid bacteria (LAB) were isolated from twenty-nine kurut samples and fifteen traditional fermented mongolian cattle milk (FMCM) samples in Tibet, China. All of the strains were isolated and divided into bacilli or cocci by phenotype, and then differentiated by restriction fragment length polymorphism (RFLP) analysis using a set of restriction enzymes, AluI, HaeIII, BsmaI, TspRI and HinfI. Restriction pattern analyses indicated that the lactobacilli could be clearly identified at the species level and the LAB cocci at the genera level by the five restriction enzymes. Further studies on 16S rDNA sequences of representative and undefined strains showed that the combination of RFLP analysis of polymerase chain reaction (PCR) for amplifying 16S rDNA and 16S rDNA sequence analysis is rapid, easy to perform, and effective for large-scale preliminary identification of LAB.