Assessment of the Sequential Simulated Gastrointestinal Tolerance of Lactic Acid Bacteria from Kefir Grains by Response Surface Methodology

ABSTRACT:  The tolerance of lactic acid bacteria (LAB) from kefir grains to gastrointestinal tract conditions was evaluated  in vitro . The effects of pH values and bile salts on the viability of LAB were investigated. The results demonstrated that pH value showed a significant effect on the viability. The viable counts exhibited a reduction of 1.5 to 2 log cycles in 0.3% to 0.5% bile salts after 4 h. The viability of LAB exposure to sequential simulated gastric and intestinal juices was assessed by response surface model (RSM). RSM indicated that the gastric pH and gastric contact time significantly affected the viability ( P  < 0.05), while the effect of intestinal contact time was not significant. Moreover, RSM revealed the interactions of pH and gastric contact time, and of pH and intestinal contact time. The LAB cells, temporarily damaged by the low pH of gastric juice (pH < 2), could recover in the intestinal juice; and the longer the intestinal contact time, the higher the viability of LAB. RSM proved to be a useful and accurate method to predict the viability of LAB under certain laboratory conditions by the model validation. This study indicated that LAB from kefir grains exhibited excellent tolerance to sequential simulated gastrointestinal tract conditions, and that kefiran possessed a significant protective effect on LAB in hostile environments.     

基于主成分分析的玉米DDGS物理特性评价

为对玉米DDGS的物理特性进行分析及量化评价,以国内外8个玉米DDGS为试验材料,测定分析其容重、热物理特性、摩擦特性、粉碎特性及色差指标参数,并运用主成分分析法简化物理特性指标,构架评价体系,得到每种样品的综合得分。结果表明:样品各物理特性指标间存在不同程度的差异;各物理特性指标之间存在不同程度的相关性,比热与热导率呈极显著正相关,与导温系数呈极显著负相关;热导率与平均粒径呈显著正相关;导温系数与容重呈极显著负相关;摩擦系数与休止角呈极显著正相关,与平均粒径呈极显著负相关;L*、b*与平均粒径呈极显著正相关;L*与b*呈极显著正相关。通过主成分分析提取了3个主成分,累积方差贡献率达到87.415%;主成分分析的结果表明进口玉米DDGS的物理特性较好。     

The influence of porosity of the grain medium on the flavour formation of Chinese liquor during solid‐state fermentation

Solid‐state fermentation is a unique technology used for Chinese liquor production and the porosity of the grain medium is one of the important characteristics in the process. However, research on the effects of porosity on flavour generation of liquor in fermented grains is rarely reported. Therefore the present paper introduces the concept of porosity from the field of soil studies and establishes a method for determining the porosity of the fermentation grain medium. Based on the practicality in liquor production, the influence of the addition levels of rice husk and the grinding intensity of the raw material on the porosity of the grain medium was studied. On this basis, the process of solid‐state fermentation was simulated and the influence of different porosities on liquor flavour production was examined. The results showed that there were obvious differences in the flavour profiles of the fermented grains with different porosities. The most abundant content and species of volatile compounds appeared when the porosity of the fermented grain medium was ~33%. The development patterns of volatile flavour compounds, in both varieties and quantities, were examined in relationship to the porosity of the fermentation medium. Copyright © 2016 The Institute of Brewing & Distilling     

Modelling of mechanical properties of five maize varieties at critical processing conditions in the production of fermented slurry-ogi

This research work was conducted to investigate the impact of critical processing conditions on the selected mechanical properties of maize in the production of fermented ogi slurry. Five varieties of maize (A4W, C3Y, D8W, B2Y, and E9W) were soaked at 28 ^ºC and average hot soaking at 65^ºC, respectively, for 96 h at 12-h interval. Selected mechanical properties were evaluated based on a 5 × 2 × 9 factorial design (varieties× soaking methods× soaking periods). Force (FB) and energy required to break (EB) maize grains decreased significantly (p < 0.05) up to the 12th hour. The EB reduced from 873.3 to 70.0 N mm and from 873.3 to 77.8 N mm for variety E9W at soaking conditions of 28^ºC and 65^ºC, respectively. Similar trends were observed for other maize varieties. Modulus of elasticity and resilience decreased significantly (p < 0.05) with increase in soaking period and moisture content. The EB to break maize grains was directly proportional to the product of Young’s modulus and area (E_m A^1.5), the FB and area (F_m A°^.5) and force required to break and geometric mean diameter (F D_g²) of maize grains with a high R² (0.9610.999). This study suggested that the duration of soaking between 12 and 24 h should be enough to significantly (p > 0.05) reduce the hardness, force, and energy required to break whole maize grains in the production of this fermented product and relevant for predicting minimum required energy for a large-scale operation.     

Effects of explosion puffing on the nutritional composition and digestibility of grains

The objective of this study was to investigate the effects of explosion puffing on the nutritional composition, physical properties, and digestibility of grains including millet, barley, black rice, rice, glutinous rice, and wheat. Explosion puffing of grains resulted in the nutritional composition with higher total sugar content and lower moisture, starch and fat contents. Although the protein content scarcely changed comparing with the untreated grains, the solubility declined significantly. Moreover, explosion puffing could significantly improve the physical properties including the water absorption index, water solubility index and gelatinization degree. The in vitro digestion experiment was employed to investigate the influences of explosion puffing on the starch hydrolysis rate and free amino acid content, and it was indicated that the digestibility of the starch and protein in grains was highly improved. The results demonstrated that explosion puffing is a suitable technique to improve the physical properties and digestibility of grains, which provided the theoretic foundation for the use of explosion puffing technology in coarse cereal processing.     

粮食污染物的快速检测技术研究进展

我国粮食安全的主要污染物包括真菌毒素、重金属和农药残留, 每年由此损失的粮食达几千万吨。为保障人民群众“舌尖上的安全”, 满足我国粮食收购、监管的实际需求, 建立和发展检测粮食中有毒有害物质的有效快速检测技术非常必要。本文系统地介绍了国内外粮食污染物的主要快速检测技术, 包括免疫检测技术、电化学分析方法、X-射线荧光光谱技术、酶抑制法和表面增强拉曼光谱法等。通过对这些快检方法应用及优缺点分析, 以期能为我国粮食污染物的有效监管及检测技术的发展方向提供有价值的参考。     

野刺梨营养酒饮料的研制

用酒糟酒、野刺梨果汁、蜂花粉、香精为原料,通过正交试验,探索含酒营养果汁饮料的生产工艺,并对蜂花粉的破壁工艺进行了探讨。实验结果显示,花粉用曲霉培养,在pH5.4、温度55℃、10%NaCl条件下降解56h,破壁率达98.5%以上。由酒糟酒降度实验可知:用1.35mg/100ml海藻酸钠和180mg/100ml可溶淀粉联合处理20°加浆酒,18h可沉淀完全,除去大部分高级脂肪酸酯。     

酱香型酒糟醅酵母菌的初步分类及选育

对酱香型酒糟醅中的酵母菌进行了初步分类和优育酵母菌株的选育,结果表明:①酱香型酒糟中的酵母可分为5类,以2类和3类酵母最多,其次是4类酵母,1类和5类酵母均很少.②从3类酵母中选育出了5株发酵力强的菌株,其中5S26和5S32耐酒精能力达19%vol,5S4在温度为46℃水浴中处理48h,仍能良好地生长.③选育出的5S32酵母在主要酿酒原料(玉米、高粱、大米、红薯和小麦)糖化液中均表现出较强的发酵力.     

微囊化纯培养发酵剂发酵奶与藏灵菇奶的比较研究

利用从藏灵菇中分离出的优势菌,进行混合发酵,比较了这种纯培养菌种发酵的酸奶与藏灵菇发酵奶在感官、主要风味成分以及优势菌株数量的差异。HPLC检测结果表明,这2种发酵奶的乳酸产量分别为7.62 g/L和7.85 g/L,无显著差异;GC检测结果表明,微囊化纯培养发酵剂发酵奶中丁二酮的含量明显高于传统藏灵菇奶;GC-MS检测结果表明,2种发酵奶中挥发性风味成分有90%相同;感官评定表明微囊化纯培养发酵剂发酵奶的可接受程度显著高于藏灵菇奶。表明,微囊化纯培养发酵剂发酵奶既保持了藏灵菇奶原有的特征,又在风味上得到了进一步的提高,表明微囊化纯培养发酵剂可以替代藏灵菇进行这类发酵奶的规模化生产。