用制糖米渣制备脱苦蛋白肽的研究

采用胰蛋白酶和含有外切酶的复合蛋白酶同时酶解脱糖米渣,制得脱苦蛋白肽产品。采用凯氏定氮法测定所得脱苦蛋白肽的蛋白质含量,并用甲醛滴定法测定其水解度。结果表明,脱苦蛋白肽产品中蛋白质含量大于88%,水解度达19%。     

不同酶嫩化处理对牛肉物性的影响

本实验以牛肉为原料,利用TA-XT2i物性测定仪,研究了蛋白酶嫩化处理对牛肉及其制品物性的影响。结果表明:三种蛋白酶处理都能够较好地保持牛肉的持水力,复合蛋白酶、胰蛋白酶和木瓜蛋白酶处理后牛肉的持水力分别比对照牛肉高28.3%、11.1%和15.9%。另外,蛋白酶处理显著降低了牛肉的烹饪失水率、剪切力、咀嚼性、弹性、回复性、黏聚性等物性指标。其中,复合蛋白酶嫩化处理的效果优于胰蛋白酶及木瓜蛋白酶。显微照相表明酶作用后牛肉肌原蛋白被分解,肌原纤维断裂,肌纤维结构完整性的破坏可能是导致牛肉上述物性变化的主要原因。     

分光光度法测定中性蛋白酶活力的不确定度分析

采用722型分光光度计按照SB/T 77300317-1999中的方法对米曲霉曲料进行中性蛋白酶的测定;通过对数学模型的分析认为样品重复性、定量器具、分光光度计、标准曲线等带入不确定度.分光光度法测定中性蛋白酶的扩展不确定度U为113μg/g,有效自由度为∞,置信区间为95%.     

Biochemical characterisation of MX-4, a plant cysteine protease of broad specificity and high stability

A new proteinase, mexicain-IV (MX-4), has been purified to homogeneity from the latex fruits of Jacaratia mexicana (formely Pileus mexicanus), a plant member of the Caricaceae family. MX-4 shows a Mr of 23.7 kDa, pI of 9.3 and maximum proteolytic activity on casein and BAPNA at pH 8.0–8.5 and pH 7.0–7.5, respectively. The amino acid sequence of MX-4 and its reversible inhibition by HgCl₂ show that the proteinase belongs to the family of cysteine proteinases. This enzyme exhibits rather broad substrate specificity, although there seems to be a slight preference for cleavage of peptides having certain hydrophobic residues in the P2 position. Biochemical and circular dichroism studies revealed that this enzyme belongs to the α + β class of proteins, in agreement with the results obtained by X-ray crystallographic structure determination, and showed that MX-4 has a higher pH and thermal stability than other members of the Caricaceae family, including papain. These properties make this novel protease a suitable novel analytical tool for the proteomic analysis of peptide fragments of great potential interest in the food industry and other industries.     

Characterization and ecological implications of midgut proteolytic activity in larvalPieris rapae andTrichoplusia ni

In their larval luminal midgut fluid,Trichoplusia ni (Lepidoptera: Noctuidae) andPieris rapae (Lepidoptera: Pieridae) contain endopeptidases as their primary proteases. Neither species has detectable exopeptidase activity. Studies using enzyme-specific substrates and inhibitors demonstrate that the endopeptidases are serine proteinases (both trypsinlike and chymotrypsinlike) with histidine at the active site. Optimal pH for the tryptic and chymotryptic activity is 8.5 and 8.0, respectively, forT. ni. and 8.0 and 9.0, respectively, forP. rapae. The efficiency of proteolytic digestion (as measured by the rate of in vitro digestion of a standard protein by the midgut luminal fluid) is positively correlated with the larval dietary protein requirement and is significantly influenced by the ratios of tryptic to chymotryptic activity present in the gut lumen of these two species of Lepidoptera.     

Myofibril-Bound Serine Proteinase (MBP) and its Degradation of Myofibrillar Proteins

Proteolysis of a myofibril-bound serine proteinase (MBP) from carp Cyprinus carpio on myofibrillar proteins and their gel formation ability were investigated. MBP readily decomposed myosin heavy chain as indicated by SDS-PAGE. In the preparation of kamaboko, the gel formation ability was diminished by addition of MBP. The optimum degradation temperatures of MBP to myosin heavy chain in myofibril and kamaboko gel were 55°C and 60°C, respectively. The degradation effects of MBP on actin, α-actinin and tropomyosin were studied by the immunoblotting method. Because of its myofibril-bound and myofibrillar protein degradation characteristics, MBP was regarded as the proteinase most probably involved in the modori effect.     

酸性蛋白酶用于酒精浓醪发酵的研究

在料水比为１∶２．８～３．２的酒精浓醪发酵中,添加适量的酸性蛋白酶,可缩短发酵周期至４８ｈ,其原料出酒率为３２．５１％,比对照提高约１．０４％,吨酒精可节省玉米用量１０２ｋｇ,成本降低约９１．８元,经济效益十分显著     

Comparison of muscle proteolytic and lipolytic enzyme levels in raw hams from Iberian and White pigs

Muscle enzyme activities in Biceps femoris from Iberian and White crossbreeds were quantified in vitro to determine possible differences due to crossbreed and the different slaughtering age (12-month-old Iberian pigs and 6-month-old White pigs). Large differences were found between proteolytic and lipolytic enzyme levels from the skeletal muscle of Iberian pig breed and White pig crossbreed. In raw hams from Iberian pig, calpain and cathepsin (B, L and H) were significantly lower, while cathepsin D was significantly higher than in White pigs. Significantly lower dipeptidyl peptidase (II and IV), aminopeptidase B, leucyl and pyroglutamyl aminopeptidase activities were found in Iberian pig breed compared with White pig crossbreed. Significantly higher levels of dipeptidyl peptidase III and alanyl aminopeptidase and lower activities of acid lipase and neutral esterase were found in Iberian breed. It was concluded that lower muscle enzyme activities and in consequence slower proteolysis and lipolysis should be desirable to obtain higher quality in dry-cured products. © 1998 SCI     

Biochemical properties of two isoforms of trypsin purified from the Intestine of skipjack tuna (Katsuwonus pelamis)

Two trypsins (A and B) from the intestine of skipjack tuna (Katsuwonus pelamis) were purified by Sephacryl S-200, Sephadex G-50 and DEAE-cellulose with a 177- and 257-fold increase in specific activity and 23% and 21% recovery for trypsin A and B, respectively. Purified trypsins revealed a single band on native-PAGE. The molecular weights of both trypsins were 24 kDa as estimated by size exclusion chromatography and SDS–PAGE. Trypsin A and B exhibited the maximal activity at 55 °C and 60 °C, respectively, and had the same optimal pH at 9.0. Both trypsins were stable up to 50 °C and in the pH range from 6.0 to 11.0. Both trypsin A and B were stabilised by calcium ion. Activity of both trypsins continuously decreased with increasing NaCl concentration (0–30%) and were inhibited by the specific trypsin inhibitors – soybean trypsin inhibitor and N-p-tosyl-l-lysine chloromethyl ketone. Apparent K_m and K_cat of trypsin A and B were 0.22–0.31 mM and 69.5–82.5 S⁻¹, respectively. The N-terminal amino acid sequences of the first 20 amino acids of trypsin A and B were IVGGYECQAHSQPPQVSLNA and IVGGYECQAHSQPPQVSLNS, respectively.     

酶法改善卵白蛋白起泡性

采用碱性蛋白酶对卵白蛋白进行酶法改性处理以改善其起泡性。探讨酶解时间、底物质量分数、酶用量因素对卵白蛋白起泡性和泡沫稳定性的影响,在单因素试验基础上采用Box-Behnken中心组合试验设计优化酶法改性条件。结果表明,碱性蛋白酶酶法改性卵白蛋白改善其起泡性的最佳条件为：酶用量144 000 U/g、底物质量分数1.90%、酶解时间34 min。在此条件下酶法改性后卵白蛋白起泡性达202.0%,为未改性（120%）的1.683 倍。