Flow properties of table margarine prepared from lipase-catalysed transesterified palm stearin:palm kernel olein feedstock

The flow properties of an experimental table margarine prepared from Rhizomucor miehei lipase-catalysed transesterified palm stearin:palm kernel olein (PS:PKO) blend at 40:60 was stored for 3 months at test temperatures of 20 and 30°C and determined using a controlled-rate rheometer. A commercial table margarine was used as a comparison. The shear stress-shear rate data was represented well by the Herschel–Bulkley model (r > 0.99). The mean yield stress values during storage were the highest for the experimental table margarine. However, the effect of storage on the mean yield stress was insignificant (p > 0.001). The Power Law model with a yield stress also represented the margarine flow well (r > 0.99) and the Power Law intercepts and slopes were also the highest for the experimental margarines, indicating a higher degree of firmness in the experimental samples. Storage effect was also insignificant (p > 0.05).     

华根霉脂肪酶催化合成乙酸香茅酯的研究

研究了华根霉菌丝结合脂肪酶(RCL)非水相直接酯化合成乙酸香茅酯的反应条件。在醇酸比为1.2∶1,反应温度40℃时得到较高的转化率。但由于底物乙酸较强的抑制性,使得高底物浓度下RCL催化能力受限。通过采用分批流加的方法使在底物浓度0.2mol/L时转化率提高至94%。与10种商品化脂肪酶进行了比较,发现在相同条件下RCL表现出较高的转化效率。产物乙酸香茅酯的色泽好,气味纯正。     

Performance of a lipase-catalyzed transesterified palm kernel olein and palm stearin blend in frying banana chips

The frying performance of an enzymatically transesterified palm stearin and palm kernel olein (1:1 by weight) blend was compared with its control (physical mixture or no enzyme added) and a commercial plastic frying shortening (CS). The samples were used as deep-fat frying media at 180°C for banana chips for seven consecutive days. The samples were then analysed for iodine value (IV), free fatty acid (FFA) content, peroxide value (PV), thiobarbituric acid (TBA) value, p-anisidine value (AV), total polar compounds (TPC), fatty acid composition, specific extinction, E^1%_1cm at 233 and 269 nm, polymer contents, viscosity and colour indices. The fried banana chips were analysed for acceptability by sensory evaluations. Storage properties of the banana chips were also evaluated by trained sensory panellists and a modified TBA test. The transesterified blend was found to have significantly (P<0.05) higher IV, FFA, PV, TBA value, AV, TPC, E^1%_1cm at 233 and 269 nm values, polymer content, viscosity and colour indices compared to the control, indicating that the transesterified blend was more susceptible to oxidative deterioration during deep-fat frying. CS generally showed the largest changes in most of the parameters, basically due to its high polyunsaturated fatty acid levels. There was no significant difference (P>0.05; for all the attributes tested) between the acceptability of the banana chips fried by the transesterified and control blends. However, the banana chips fried in CS had significantly (P<0.05) lower scores in terms of flavour, aftertaste and overall acceptability. This might be due to the typical hydrogenation flavour of CS. In the storage stability study of the banana chips, it was found that the banana chips fried in the transesterified blend were significantly (P<0.05) more rancid (lower score in sensory evaluations) and had a higher TBA value at the end of the storage time than the control.     

Use of lipase from Rhizomucor miehei in dry fermented sausages elaboration: Microbial, chemical and sensory analysis

Three different amounts of lipase (0.075, 0.100 and 0.150 LU/g) from Rhizomucor miehei (Palatase M 200L Novo Nordisk) were used to determine the correct amount to use in dry fermented sausages. Determination of acidity values through fourteen days of ripening showed that 0.100 LU/g was the most appropriate. Two types of fermented sausages were manufactured, addition of the enzyme being the only difference between them. Addition of Palatase did not affect product stability (pH and A(w)), and the growth of micro-organisms. In spite of the increase in acidity value, no rancidity developed as determined by both chemical and sensory analysis. Increases in the liberation of palmitic, palmitoleic, stearic, oleic and linoleic acids were found when lipase was used. Juiciness and taste were slightly better in the sausages with Palatase than in those without, but these differences were not reflected in the overall acceptability.     

Hydrolysis of bovine milk fat globules by lipoprotein lipase: inhibition by proteins extracted from milk fat globule membrane

Extraction of membrane proteins from milk fat globules by GuHCl or by MgCl2 made the lipids more accessible to lipolysis by added lipoprotein lipase. The increase in lipolysis paralleled the loss of membrane proteins and was continuous up to 2.5 M GuHCl, which was the highest concentration used. About twice as much protein was extracted with 2.5 M GuHCl as with buffer only. The amount of protein lost was about 50% of total milk fat globule protein. Lipolysis of milk fat globules was inhibited by addition of the extracted protein. The extracted proteins also reduced lipolysis when added to whole milk. More protein was needed to inhibit lipolysis of milk fat globules treated with GuHCl compared with globules treated with buffer only. The inhibition by a given amount of protein decreased if more milk fat globules were used. Protein extracted with MgCl2 had similar effects as those extracted with GuHCl. The major components extracted with MgCl2 migrated in the 40 to 50-kdalton region on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By gel filtration chromatography, two protein fractions were obtained, which inhibited lipolysis more efficiently than the total extract. As has previously been found for inhibition of lipolysis by skim milk, the amount of extracted protein needed to inhibit lipolysis varied between preparations of milk fat globules. Milk with propensity to cold-induced ("spontaneous") lipolysis was normalized by addition of extracted proteins.     

Influence of buffer and l-phenylalanine concentration in the Rhizomucor miehei lipase catalysed synthesis of l-phenylalanyl-d-glucose ester investigated through response surface methodology

Reaction conditions for Rhizomucor miehei lipase (RML) catalysed synthesis of l-phenylalanyl-d-glucose using unprotected l-phenylalanine and d-glucose were optimized using response surface methodology (RSM). A central composite rotatable design (CCRD) was employed involving 32 experiments of five variables (l-phenylalanine concentration in mmol, amount of RML in mg, pH, incubation period in h and buffer concentration in mM) at five levels. A second-order polynomial equation was developed in terms of linear, quadratic and cross product terms to study the effects of variables on esterification yields. A R ² value of 0.7 was obtained for this complex reaction. From the surface and contour plots it was found that higher yields were observed for a very narrow pH range of 4.5–6.5 at l-phenylalanine concentrations above 3 mmol. The extent of esterification decreased with increase in RML concentration for incubation periods below 60 h. However, longer incubation periods above 60 h, enhanced esterification at all RML concentrations. Lower conversions below 0.5 mmol required less than 3.5 mmol l-phenylalanine concentration and a broad range of buffer concentration from 0.1 mM (0.1 ml, 0.1 M buffer of pH 6.0) to 0.5 mM (0.5 ml, 0.1 M buffer of pH 6.0). However, higher conversions from 0.6 to 0.8 mmol required a buffer concentration above 0.25 mM (0.25 ml, 0.1 M buffer of pH 6.0) at l-phenylalanine concentrations above 3.5 mmol. An optimum predicted yield of 1.01 mmol for l-phenylalanyl-d-glucose at 3 mmol l-phenylalanine, 100 mg of RML, 24 h incubation period, 0.5 mM (0.5 ml of 0.1 M buffer), pH 4.8 acetate buffer was found to agree with 0.97 mmol obtained under these experimental conditions. Validation experiments carried out under random conditions also exhibited good correspondence between predicted and experimental yields.     

Physical properties of cream reformulated with fractionated milk fat and milk-derived components

Emulsifying properties of milk-derived components influence the physical characteristics of reformulated creams. Fractionated butter oils with different melting ranges (low-melt: 10 to 25 degrees C; medium-melt: 25 to 35 degrees C) were recombined into fluid dairy systems using skim milk, or sweet buttermilk and butter-derived aqueous phase to manufacture 20% milk fat creams. Separation temperature (49 degrees C or 55 degrees C) in obtaining emulsifying components was examined for its effect on physical properties of pasteurized reformulated creams. Rate of creaming, viscosity, feathering, and sensory characteristics of reformulated and natural creams stored at 3.3 degrees C were evaluated over a 13-d period. Creaming rate of reformulated and natural creams was unaffected by formulation and was most influenced by duration of storage. Melting characteristics of butter oils influenced viscosity at some shear rates. With the exception of natural cream, all formulations were consistent in apparent viscosity during the 2-wk storage period. All creams feathered in a pH range of 4.70 to 5.20 and were classified as moderately stable to slightly unstable. All reformulated and natural creams met sensory quality specifications with the exception of creams formulated with skim milk and lower melting range butteroil. Creams formulated with buttermilk, butter-derived aqueous phase, and lower-melting range butter oil most closely mimicked natural creams with regard to sensory quality and viscosity.     

粗状假丝酵母脂肪酶的分离纯化及水解乳脂的初步研究

从粗状假丝酵母诱变株发酵液中,经双水相萃取、丙酮沉淀、DEAE-Sepharose FF阴离子交换层析和Phenyl-Sepharose FF疏水层析,得到电泳纯的脂肪酶,纯化倍数为20.81,活力回收率为19.8%,亚基相对分子质量约为56.6ku。研究了粗状假丝酵母脂肪酶水解天然乳脂的工艺条件,得出其水解乳脂适宜温度为45℃,缓冲体系pH值为8.0,反应21h,乳脂水解率达到最佳,并通过GC-MS分析鉴定了水解产物中主要的致香成分。     

Use of Mucor miehei lipase to improve functional properties of yolk-contaminated egg whites

Egg yolk contamination of egg whites continues to be a serious problem in the egg industry. The ability of egg whites to form stable and voluminous foams is greatly inhibited by yolk contamination, even at very low levels, between 0.01% and 0.2% w/w yolk in white. Experiments were conducted to determine if Mucor miehei lipase could regenerate the functional properties of yolk-contaminated egg whites. Lipase from M. miehei and colipase from porcine pancreas were added to yolk-contaminated (0.2%, w/w) egg white samples to hydrolyze triglycerides originating from egg yolk. Enzymatic hydrolysis of triacylglycerols was confirmed using thin-layer chromatography. Treatment of yolk-contaminated samples with lipase and colipase yielded significant (P < 0.05) improvements in a number of the functional properties, including the final foam volume, foam capacity, and foaming power. These functional properties showed complete restoration to control levels. However, foam stability and foam drainage levels were not statistically different from yolk-contaminated samples that had not been enzymatically treated. Enzyme-treated yolk-contaminated egg whites were also tested in angel food cakes. Enzyme-treated, yolk-contaminated egg whites performed similarly to non-yolk-contaminated control, and much better than yolk-contaminated sample in angel food cakes. The results show that most negative effects of yolk contamination can be reversed by treatment with Mucor miehei lipase and colipase.     

Kinetic analysis of isothermal crystallization in hydrogenated palm kernel stearin with emulsifier mixtures

The kinetics of isothermal crystallization of hydrogenated palm kernel stearin (HPKS) with emulsifiers was evaluated by applying the Avrami equation. Effects of five commercial emulsifiers (lecithin, monoglyceride, polyglycerol polyricinoleate, Span 60, and Tween 60) on crystallization behaviors were tested at four different isothermal temperatures (15, 20, 25, and 30 °C). It is shown that, as temperature increases, induction time for HPKS samples generally increased especially from 25 to 30 °C. Meanwhile, different nucleation mechanisms were observed according to Avrami exponent (n) values. The addition of emulsifiers generally accelerated crystallization rate without changing the growth mechanism (plate-like growth) under 25 °C. However, when the temperature increased to 30 °C, n ranged from 1.0 to 5.1, which indicated different nucleation mechanisms induced by different emulsifiers. Avrami constant (k) (indicating the crystallization rate) decreased as the temperature increased except for samples with Span 60. At higher temperatures, values of t_1/2 were significantly higher which reflects the decrease in k at higher temperatures. Crystal microstructures at 30 °C were obtained by using polarized light microscope. Lecithin and Span 60 samples showed large and dense crystals compared with the control sample. Tween 60 sample showed very small crystals which aggregated in a line trend. However, small differences were observed in fractal dimension results except for Tween 60 sample.     

Detection of foreign fat in milk fat II. Quantitative evaluation of foreign fat mixtures

Summary Based on gas chromatographic analysis of triacylglycerol composition of 755 different milk fat samples, formulae were derived from statistical evaluations. They allow quantitative detection of greatly differing foreign fat additions to milk fat by insertig defined triacylglycerol contents of a fat to be analyzed. Further, any combination of different foreign fats, consisting. e.g., of a mixture of medium- and long-chain triacylglycerols can be detected by using this method. For the widely varying foreign fat mixtures, limits of detection between 2–5% were established. For 23 different additions (3–15%) of individual vegetable foreign fats or animal depot fats, as well as for 33 foreign fat mixtures (4–7% addition) added to unknown milk fats from varying feeding periods, absolute mean deviations of 0.7–0.8% were found.

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Fremdfettnachweis in Milchfett II. Quantitative Bestimmung von Fremdfettgemischen

Zusammenfassung Basierend auf der gaschromatographisch bestimmten Triglyceridzusammensetzung von 755 verschiedenen Milchfettproben sind mit statistischen Auswertungen Triglyceridformeln abgeleitet worden, die durch das Einsetzen bestimmter Triglyceridanteile eines zu prüfenden Fettes den quantitativen Nachweis verschiedenster Fremdfettzusätze zum Milchfett zulassen. Darüber hinaus können mit der Methode auch beliebige Kombinationen verschiedener Fremdfette, die z. B. aus einer Mischung von mittel- und langkettigen Triglyceriden bestehen, nachgewiesen werden. Für die verschiedensten Fremdfettgemische ergaben sich Nachweisgrenzen von 2–5%. Bei 23 unterschiedlichen Zusätzen (3–15%) einzelner pflanzlicher Fremdfette oder von tierischen Depotfetten sowie von 33 Fremdfettgemischen (4–7% Zusatz) zu unbekannten Milchfetten aus verschiedensten Fütterungsperioden wurden absolute mittlere Abweichungen von 0,7–0,8% festgestellt.

     

Assessment of lipoprotein activators of skim milk lipoprotein lipase and the relationship between lipoprotein lipase activity and milk fat synthesis

Bovine plasma and lipoproteins isolated by gel filtration chromatography were examined for their ability to activate skim milk lipoprotein lipase. Addition of equal amounts of protein from either triglyceride-rich lipoprotein, low density lipoprotein, high density lipoprotein or plasma to a lipoprotein lipase assay resulted in 6.0, 2.2, 2.5, or 1.1% hydrolysis of radiolabelled triglyceride emulsion. Lipoprotein lipase activity in skim milk was evaluated as an indicator of mammary lipid secretory capacity. Skim milk lipoprotein lipase activity was significantly lower immediately prepartum as compared with activity immediately postpartum (.2 vs. 5.4% of substrate hydrolyzed). Skim milk lipoprotein lipase was significantly higher during the final 12 d of lactation than in samples obtained 12 d after machine milking was terminated (5.6 vs. less than 1% of substrate hydrolyzed). Although skim milk lipoprotein lipase activity appeared positively related to mammary lipid secretory capacity during the time immediately surrounding initiation and cessation of copious milk production, activity between those periods was not correlated to milk fat percentage, milk fat yield, or stage of lactation.     

Health promoting properties of protein hydrolysates produced from oil palm (Elaeis guineensis) kernel

This study aimed to determine the lipid-lowering properties, antioxidant capacity (AC) and angiotensin-I converting enzyme (ACE)-inhibitory activity of oil palm kernel protein hydrolysates (OPKHs) that were produced using protease and pepsin-pancreatin hydrolysis. The effects of the OPKHs on apolipoprotein B (apoB) secretion was assessed using HepG2 cells as a model and the AC of the OPKHs was determined based on ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP). Both protease and pepsin-pancreatin hydrolysates reduced apoB secretion significantly (p<0.05). The OPKHs scavenged ABTS radicals effectively and demonstrated a high reducing power even at a low concentration (1 mg/mL). The AC of the OPKHs was significantly correlated with the OPKHs protein content. However, the OPKHs demonstrated very low ACE-inhibitory activity. The pepsinpancreatin hydrolysate demonstrated significant lipidlowering properties, favourable AC and ACE inhibitory activity in compared to protease hydrolysate. Therefore, OPKH demonstrate the potential as a nutraceutical for functional foods.     

The absence of endogenous lipase from oil palm mesocarp

Oil palm (Elaeis guineensis Jacq.) fruit mesocarp had higher levels of free fatty acids at the ends of the fruits than in the middle, and microscopy showed that yeasts penetrate the mesocarp via the scars at each end. Very low levels of esterase activity, probably not due to a lipase, were detected in mesocarp extracts by using 4-methyl umbelliferone esters as substrates, but no activity against triacylglycerols could be found. In bruising and storage trials, the only variable that correlated (P<0.01) with free fatty acid level was yeast and mould count. It is concluded that yeasts and moulds are the source of lipolytic activity in oil palm mesocarp, and there is no evidence for an endogenous lipase.     

微小毛霉与米黑毛霉凝乳酶的制备及其凝乳质构特性研究

将经乙醇分步沉淀所制得的微小毛霉和米黑毛霉凝乳酶以小牛皱胃酶为对照在不同温度、不同时间和不同pH值下凝乳,以下压过程的平均力为衡量标准,对其物性进行了比较,得出在相同条件下,米黑毛霉凝乳酶的凝乳要好于微小毛霉凝乳酶,并在高温和酸性环境要比微小毛霉凝乳酶稳定。     

固定化脂肪酶催化酯交换制备母乳脂肪替代物

椰子油、橄榄油和大豆油按质量比0.3∶0.2∶0.5比例混合,制备富含不饱和脂肪酸的混合脂肪酸。以Sn-2位富含棕榈酸的猪油和混合脂肪酸为底物,通过固定化脂肪酶Lipozyme TL IM的酯交换作用制备母乳脂肪替代物。经单因素试验确定最佳反应条件为:猪油与混合脂肪酸质量比1∶2.0,加酶量10%,反应温度65℃,反应时间8 h。反应产物甘油三酯总脂肪酸组成及Sn-2位脂肪酸组成与母乳脂肪相似。     

Determination of butanoic acid in milk fat and fat mixtures containing milk fat: a comparison of methods

Council Regulation (EC) No. 2991/94 has created an urgent need for a reliable method to quantify the milk fat content in spreadable fats containing milk fat. As the butanoic acid concentration is the most promising indicator for the presence of milk fat in a fat blend, a reference method for its determination is required. Three analytical approaches to quantify butanoic acid by gas-liquid chromatography, i.e. determination by free butanoic acid, by methyl butanoate, and by headspace sampling, have been compared. A reference material (anhydrous milk fat) having a certified content of butanoic acid was used to check the accuracy of the methods. All methods tested were well within the uncertainty range of the certified value. The methyl butanoate method had highest precision, followed by the free butanoic acid method and the headspace sampling procedure. Relative standard deviations for repeatability were 0.38, 0.86 and 1.48, respectively. The headspace method had the highest sample throughput (8 samples h⁻¹), while the methyl butanoate allowed only one sample h⁻¹ to be analysed.