超临界条件下油脂氢化研究进展

近年来,反式脂肪酸带来健康问题日益引起人们关注,过多摄入反式脂肪酸将会引发心血管等多种疾病,而油脂氢化过程是产生反式脂肪酸主要来源之一;在超临界条件下进行油脂氢化可大大减少反式脂肪酸形成,已成为当前研究热点。该文主要介绍超临界流体特性及其在油脂氢化工艺中应用。     

Effect of different rumen-inert fatty acids supplemented with a dietary antioxidant on performance and antioxidative status of early-lactation cows

The objective of the study was to evaluate the effect of diets supplemented with fatty acids of different degrees of saturation, in the absence or presence of an antioxidant (AOX; Agrado Plus, Novus International Inc., St. Charles, MO), on dairy cow lactation performance. Calcium salts of long-chain fatty acids were supplemented as a source of lower saturation fatty acid, and a palm acid product was supplemented as the higher saturation fatty acid source. Sixty early-lactation Chinese Holstein cows (100 ± 23 d in milk) were randomly allocated to 4 dietary treatments in a 2 × 2 factorial design: (1) lower saturation fatty acid (LS), (2) LS and AOX, (3) higher saturation fatty acid (HS), and (4) HS and AOX. The Ca salts of long-chain fatty acids and palm acid product were supplied at 1.8 and 1.5% on a dry matter basis, respectively, to form isoenergetic diets. The AOX was added at 0.025% in the ration. The experiment lasted 9 wk, including 1 wk for adaptation. Lactation performance was recorded and milk was sampled and analyzed weekly. Blood samples were taken from the coccygeal vein to determine metabolism parameters on d 16, 36, and 56 during the experiment. Neither fatty acid type nor AOX supplementation showed a significant effect on dry matter intake during the study. Milk yield was lower in the LS-fed cows compared with the cows fed HS. Milk fat and milk protein concentrations were not affected by fatty acid type or AOX supplementation. Adding AOX increased the yield of milk in the LS-fed cows, but did not affect those fed HS. Activity of plasma superoxide dismutase was significantly lower, plasma glucose tended to be lower, and plasma malondialdehyde was higher in the LS-fed animals compared with those fed HS. Addition of AOX decreased both plasma nonesterified fatty acids and hydrogen peroxide contents and increased total antioxidant capacity across the fatty acid types. Plasma β-hydroxybutyrate was not affected by fatty acid type or AOX treatment. Cows fed LS had higher cis-9 C_18:1 and trans-10, cis-12 C_18:2 in milk at the expense of C_18:0, whereas AOX addition increased milk cis-9 C_18:1 at the expense of milk C_12:0, C_16:0, and trans-10, cis-12 C_18:2. It is inferred that feeding LS resulted in inferior lactation performance, whereas addition of antioxidant partially alleviated these negative effects.     

Effects of particle size and dry matter content of a total mixed ration on intraruminal equilibration and net portal flux of volatile fatty acids in lactating dairy cows

Effects of physical changes in consistency of ruminal contents on intraruminal equilibration and net portal fluxes of volatile fatty acids (VFA) in dairy cows were studied. Four Danish Holstein cows (121 ± 17 d in milk, 591 ± 24 kg of body weight, mean ± SD) surgically fitted with a ruminal cannula and permanent indwelling catheters in the major splanchnic blood vessels were used. The experimental design was a 4 × 4 Latin square with a 2 × 2 factorial design of treatments. Treatments differed in forage (grass hay) particle size (FPS; 3.0 and 30 mm) and feed dry matter (DM) content of the total mixed ration (44.3 and 53.8%). The feed DM did not affect chewing time, ruminal variables, or net portal flux of VFA. However, decreasing the FPS decreased the overall chewing and rumination times by 151 ± 55 and 135 ± 29 min/d, respectively. No effect of the reduced chewing time was observed on ruminal pH or milk fat percentage. Cows maintained average ventral ruminal pH of 6.65 ± 0.02, medial ruminal pH of 5.95 ± 0.04, and milk fat of 4.42 ± 0.12% with chewing time of 28.0 ± 2.1 min/kg of DM when fed short particles. The medial ruminal pool of wet particulate matter was decreased by 10.53 ± 2.29 kg with decreasing FPS, thereby decreasing the medial pool of total VFA, acetate, propionate, butyrate, isobutyrate, and isovalerate by 1,143 ± 333, 720 ± 205, 228 ± 69, 140 ± 51, 8.0 ± 2.3, and 25.2 ± 5.6 mmol, respectively. Ventral pool variables were not affected by treatments. Relatively large intraruminal differences of VFA concentrations and pH between the ventral and medial pools were observed, VFA concentrations being largest and pH being the lowest medially. This indicates that the ruminal mat acts as a barrier retaining VFA. The effects of reduced FPS were limited to the VFA pool sizes of the mat, leaving ruminal pH, ruminal VFA concentrations, and net portal flux of VFA unaffected. Consequently reduced FPS affected the intraruminal equilibration of VFA between mat and ventral rumen with an estimated turnover rate of isobutyrate increasing from 50 ± 3%/h with long particles to 61 ± 3%/h with short particles. The estimated ruminal fluid flow and therefore intraruminal VFA transport between medial and ventral phase was not affected by the FPS. In conclusion, the ruminal mat pool of VFA was proportional to the size of the mat and the only detected effects of decreasing FPS were decreasing the mat size and an increasing turnover of the mat pool of VFA.     

Inactivation of Escherichia coli O157:H7 and Salmonella spp. on alfalfa seeds by caprylic acid and monocaprylin

Alfalfa and other seed sprouts have been implicated in several Escherichia coli O157:H7 and Salmonella spp. human illness outbreaks in the U.S. Continuing food safety issues with alfalfa seeds necessitate the need for discovery and use of novel and effective antimicrobials. The potential use of caprylic acid (CA) and monocaprylin (MC) for reducing E. coli O157:H7 and Salmonella spp. populations on alfalfa seeds was evaluated. The effectiveness of three concentrations of CA and MC (25, 50, and 75 mM) to reduce E. coli O157:H7 and Salmonella spp. populations in 0.1% peptone water and on alfalfa seeds was evaluated. Surviving populations of E. coli O157:H7 and Salmonella spp. were enumerated by direct plating on tryptic soy agar (TSA). Non-inoculated alfalfa seeds were soaked for up to 120 min to evaluate the effect of CA and MC solutions on seed germination rate. For planktonic cells, the efficacy of the treatments was: 75 MC > 50 MC > 25 MC > 75 CA > 50 CA > 25 CA. Both E. coli O157:H7 and Salmonella spp. were reduced to below the detection limit (0.6 log CFU/ml) within 10 min of exposure to 75 MC from initial populations of 7.65 ± 0.10 log CFU/ml and 7.71 ± 0.11 log CFU/ml, respectively. Maximum reductions of 1.56 ± 0.25 and 2.56 ± 0.17 log CFU/g for E. coli O157:H7 and Salmonella spp., respectively, were achieved on inoculated alfalfa seeds (from initial populations of 4.74 ± 0.62 log CFU/g and 5.27 ± 0.20 log CFU/g, respectively) when treated with 75 MC for 90 min. Germination rates of CA or MC treated seeds ranged from 84% to 99%. The germination rates of CA or MC soaked seeds and water soaked seeds (control) were similar (P > 0.05) for soaking times of ≤ 90 min. Monocaprylin (75 mM) can be used to reduce E. coli O157:H7 and Salmonella spp. on alfalfa seeds without compromising seed viability.     

自制酵素中乳酸菌群动态分析及对重金属的吸附积累特性

为了分析自制酵素发酵过程中乳酸菌群动态变化,采用高通量测序技术分析了2种酵素不同发酵时段细菌群落结构及乳酸菌群丰度,并分离纯化了主要乳酸菌,测定代表性菌株对重金属Pb~(2+)和Cd~(2+)的耐受性及吸附积累量。结果表明:2种样品在整个发酵过程中菌群变化比较接近;乳酸杆菌属(Lactocacillus)在4个发酵阶段均占优势(相对丰度25.8%~70.9%),发酵20 d时相对丰度最高;种水平上不同发酵时段菌种变化较大,戊糖乳杆菌相对丰度从发酵10(22.5%~26.5%)~20 d(61.6%~65.7%)明显增加,而大肠杆菌(Escherichia coli)相对丰度急剧下降;39株乳酸菌分离菌株中戊糖乳杆菌和短乳杆菌居多;相较于Cd~(2+),3株代表菌对Pb~(2+)具有较强耐受性,其中戊糖乳杆菌AA11对Pb~(2+)去除率达78.47%。结果显示,酵素中以乳酸菌为优势菌群,发酵初期戊糖乳杆菌明显抑制大肠杆菌,并对去除食品中的Pb~(2+)有较好的应用潜力。     

利用木薯淀粉为原料发酵生产丁二酸的研究

利用木薯粉为原料发酵生产丁二酸,将先糖化后发酵(SHF)和同步糖化发酵(SSF)2种发酵模式进行比较,发现SSF发酵模式在工艺上、产量上均优于SHF,进而对SSF的一些工艺条件进行摇瓶优化,得到SSF的最适发酵温度为37℃,糖化酶添加量为1000U/g,最适底物浓度60g/L.在7L发酵罐中进行放大实验,用木薯粉同步糖化发酵45h,最终丁二酸浓度为61.2g/L,乙酸浓度为4.66g/L,生产强度达到1.36g/(L·h),丁二酸转化率为89%.     

酪蛋白水解物对乳酸菌的促生长作用

研究了酪蛋白的木瓜蛋白酶水解物对乳酸菌(嗜热链球菌∶保加利亚杆菌=1∶1)的促生长作用.通过比较不同水解度的酪蛋白水解物的增值作用,发现酪蛋白经木瓜蛋白酶水解8 h后的水解物具有最强的促进乳酸菌生长作用.本试验进一步考察了该水解物对酸乳乳酸菌代谢产物(乳酸和胞外多糖)的产量及活菌数变化的影响.结果表明木瓜蛋白酶酪蛋白水...     

杂环氨基酸酯的合成与表征

以三种杂环结构的氨基酸、二氯亚砜、甲醇/乙醇为原料,合成L-色氨酸甲/乙酯盐酸盐、L-组氨酸甲酯盐酸盐以及L-脯氨酸甲/乙酯盐酸盐,产率较高,并通过核磁共振谱、红外光谱、元素分析对其盐酸盐进行了结构表征,所得到的氨基酸酯盐酸盐分别用饱和碳酸钠溶液中和、二氯甲烷萃取,最终得到了三类杂环氨基酸酯。     

In vitro gastrointestinal digestion of liquid and semi-liquid dairy matrixes

Protein digestion in two liquid dairy matrixes with different heat treatments (pasteurized and sterilized milks) and in one semi-liquid dairy matrix (stirred-yogurt) was investigated using an in vitro gastrointestinal digestion model. After buccal digestion, significantly lower amount of soluble proteins were measured in yogurt than in both milks. This difference between dairy matrixes decreased during gastric digestion and disappeared at the end of the duodenal digestion upon the proteolytic action of pepsin and pancreatin. Electrophoresis pattern of digested mixtures showed that casein digestion began at the gastric phase and was slower for pasteurized milk than sterilized milk and yogurt. At the end of duodenal digestion, no more intact caseins were present in all the dairy matrixes while faint bands of whey proteins were still visible for pasteurized milk and yogurt. The release of free amino acids during the duodenal phase varied according to their nature (acid, basic, neutral or hydrophobic) and seems to be governed by the specificity of the enzymes. These results suggest that the severity of milk's heat treatment influences the kinetics of protein digestion, mainly during the gastric phase, and that the impact of processing has to be considered to study protein digestion in dairy products.     

酸性荧光黄73对锦纶6的染色性能

采用酸性荧光黄73对锦纶6进行染色,探讨了染色p H、染色温度、染色时间、Na Cl用量、染料用量对表观色深K/S值的影响,测试了染色织物的荧光效果和色牢度.研究结果表明:染色织物的K/S值随着染色温度的升高和染色时间的延长而逐渐增加,随着染色p H和Na Cl用量的增加而逐渐下降;染色织物具有一定的荧光强度,可满足警示服外的其他服饰的荧光要求.锦纶6的最佳染色工艺为:酸性荧光黄73用量2%(omf),染色p H=5,染色温度高于80℃,染色时间60 min.该工艺下染色的织物具有较好的耐皂洗和耐摩擦色牢度.