Production and structural characterisation of dextran from an indigenous strain of Leuconostoc mesenteroides BA08 in Whey

In this work, the production of dextran was carried out in whey‐supplemented media using Leuconostoc mesenteroides BA08. Different growth and nutritional parameters were optimised to maximise the dextran production. Batch production in whey‐based media under optimised nutritional and growth conditions yielded a dextran concentration of 17.25 g/L. Structural analysis of the purified polymer by FT‐IR, 1D ¹H and ¹³C nuclear magnetic resonance methodology revealed that polymer was a linear dextran having 93% α‐(1→6) linkage in the main chain. The morphology of the dried dextran and dextran‐producing cells was also studied by scanning electron microscope which showed a granular and porous or weblike structure, respectively. The results obtained showed that the industrial whey supplemented with nutrients such as sucrose, yeast extract and K₂HPO₄ can serve as an ideal growth medium for dextran production. The optimised fermentation and nutritional parameters can be further scaled up to establish the potential for the commercial production of food‐grade dextran from whey as part of a novel cost‐effective and environment‐friendly approach.     

婴幼儿配方食品和乳粉中维生素C的测定

目的建立一种前处理简单、仪器条件稳定、准确高效的婴幼儿配方食品和乳粉中维生素C的检测方法。方法用含有三(2-羧乙基)膦(TCEP)的三氯乙酸(TCA)对样品中的维生素C进行提取,C18柱色谱分离,流动相为含TCEP与癸胺作为离子对试剂和pH 5.4的醋酸钠的混合水溶液,然后在紫外检测器265 nm处进行检测。结果本方法的相对标准偏差(n=6)在0.36%~3.2%之间,平均回收率为88.5%~97.9%,线性相关系数r~2大于0.9999。结论本方法实验前处理简单,干扰因素少;仪器条件稳定,灵敏度高,重复性好;适合婴幼儿配方食品和乳粉复杂基质样品的测定。     

Effect of maturity, processing, and storage on the furanocoumarin composition of grapefruit and grapefruit juice

Since the early 1990's, grapefruit juice has been implicated in drug interaction with various furanocoumarins (FCs) now associated with the effect. Although FCs are present in various fruits and vegetables, it is their presence in grapefruit that has attracted the most attention. Studies have shown that FCs in grapefruit juice can vary significantly and from multiple causes. Most of all, FCs are stress-induced molecules, their levels affected by many factors ranging from UV exposure to insect infestation. There are also varietal and seasonal factors. In this study, juice processing and storage parameters were investigated. Prolonged fruit storage prior to processing and most steps involved in juice processing had little influence on the levels of 6',7'-dihydroxybergamottin (DHB), paradisin C, or bergamottin. However, products that were hot filled or stored at room temperature had lower amounts of DHB and paradisin C and higher amounts of bergaptol compared to juices that were not hot filled and stored at refrigerated temperatures. Both DHB and paradisin C are potent CYP3A4 inhibitors, while bergaptol is a very weak inhibitor. Bergamottin amounts decreased to a lesser extent. Therefore, grapefruit juice products that were hot filled or have been stored at room temperature for an extended period of time will have a reduced drug interaction potential.     

Evaluation of apple texture with contact acoustic emission detector: A study on performance of calibration models

Performance of calibration models for evaluation of apples sensory texture with contact acoustic emission detector (CAED) was studied. For model evaluation and testing, 2500 apples of 19 cultivars were harvested over two seasons. Apples were stored at normal atmosphere (NA), controlled atmosphere (CA) for different periods or were treated with 1-methylcyclopropene (1-MCP) in order to obtain a high variability of texture and fruit maturity. Apples were tested simultaneously in two distinct laboratories. The models were created and validated on averaged values from 10 fruits using simple linear regression, multiple linear regression (MLR) and principal component regression (PCR). Performance statistics of the models were expressed in terms of determination coefficient (R²), root mean square errors of cross validation (RMSECV) or prediction (RMSEP) and ratio of prediction to deviation (RPD). Firmness and total acoustic emission counts were predictors of sensory texture in the models. MLR and PCR models show better performance for prediction of sensory data than simple linear regression models however PCR models show the best results among models tested in this study. Common PCR models for several cultivars allow for successful prediction of hardness (RPD > 2.0), crispness and overall texture (1.5 < RPD < 2.0). The single-cultivar PCR models, constructed on data sets containing 26-39 averaged values, reveal significantly better performance (RPD > 2.0 for most of the cases) than the common PCR models for many varieties.     

罗汉果蛋白酶的贮存稳定性研究

将罗汉果蛋白酶粗酶以固态或液态在有光或避光、不同温度、不同浓度的半胱氨酸、乙二胺四乙酸(EDTA)和葡萄糖的条件下贮存,分别在不同时间测定粗酶的相对活力,以考察这些条件对罗汉果贮存稳定性的影响。结果表明:在这些条件下,60 d内,酶活都基本保持,但60 d后,酶失活速度加快。其中光和温度(-20℃～25℃)对罗汉果蛋白酶贮存稳定性的影响不明显,但加入半胱氨酸、EDTA或葡萄糖可减缓60 d后酶活下降的速度。所以罗汉果蛋白酶若在60 d内使用的可一般存放,若60 d后使用,可加入一定的半胱氨酸、EDTA或葡萄糖贮存,以保持其活性。     

电位滴定法测定婴幼儿配方奶粉中Vc含量

介绍了电位滴定法测定婴幼儿配方奶粉中Vc含量的方法。在试样被偏磷酸等酸性浸提剂提取后的酸性溶液中,用EDTA掩蔽干扰离子后,直接用2,6-二氯靛酚溶液滴定试样中的维生素,并利用电位滴定仪的电位突跃指示滴定终点。探讨了金属螯合剂EDTA、滴定剂浓度及酸性浸提剂对测定结果的影响。对滴定法的线性关系、回收率及精密度进行了研究,结果表明:该方法具有较好的线性和精密度,回收率为95%~101.5%,测定结果的相对标准偏差小于1.0%。该方法具有测试简便、快速、干扰少及准确等特点。     

纸浆纤维交叉分离的一种新型算法

纸浆纤维特征的有效测量将直接关系到成品纸的质量。为了准确测量纸浆纤维的长度,本文提出了一种基于数字图像处理的纸浆纤维交叉分离算法。该算法解决了在测量单根纤维长度等参数时无法对两根交叉纤维进行精确测量,产生严重误差的问题。通过Visual C++实现的交叉纤维分离的结果和大量数据,显示了这一方法的准确性和鲁棒性。     

外源因素对萌发大豆中VC含量的影响

大豆不含VC,但在萌发过程中会产生VC,且生成量随萌发天数的延长而增加。在大豆萌发过程中分别采用葡萄糖、L-半乳糖、D-甘露糖、碘化钾浸泡以及紫外光照射,研究外源因素对VC含量的影响。结果表明：葡萄糖、L-半乳糖、碘化钾溶液浸泡以及紫外光照射对VC合成均有不同程度的促进作用,其中L-半乳糖浸泡的作用最大,与未处理相比VC增加了8.43mg/100g;其次是葡萄糖浸泡,VC增加了4.23mg/100g,且较低葡萄糖质量浓度下延长浸泡时间优于高质量浓度短时浸泡。紫外光照射从第5天开始对VC合成的促进作用明显加强。     

白藜芦醇对KKAy小鼠体质量和脂肪分布的影响及机制

目的:观察白藜芦醇(resveratrol,res)对KKAy小鼠体质量和脂肪分布的影响,并探讨其中机制。方法:将36只8周龄KKAy小鼠分成3组,其中两组KKAy小鼠分别饲喂添加白藜芦醇(以饲料质量2、4g/kg添加)的AIN93G饲料,另外以12只同周龄C57BL/6J小鼠为对照。观察干预12周后白藜芦醇对小鼠体质量及皮下脂肪、附睾脂肪分布的影响;Western blot实验检测不同组小鼠附睾及皮下脂肪组织中沉默信息调节因子1(silent information regulator 1,sirt-1)、过氧化物增殖物受体γ(peroxisome proliferator-activated receptorγ,PPARγ)和CCAAT增强子结合蛋白α(CCAAT/enhancer-binding proteinα,C/EBPα)蛋白表达水平。结果:白藜芦醇干预可以在不影响摄食量的情况下减轻KKAy小鼠体质量,与模型组相比,高剂量res组小鼠体质量降低,且脂肪组织的质量及与脂肪组织系数降低;附睾及皮下脂肪组织中sirt-1的表达升高,PPARγ及C/EBPα蛋白表达水平降低。结论:白藜芦醇可以减轻肥胖小鼠...