摘要:

AbstractChemical esterification of cinnamic acids to cell walls has been proposed to simulate the negative effect of these acids on fibre digestion by ruminants. In this model a spontaneous reaction between an acid chloride and a free hydroxyl group forms an ester linkage between p‐coumaric acid (PCA), for example, and cell wall carbohydrates. This study was conducted to evaluate that system. Esterification of p‐coumaric acid (PCA) to switchgrass (Panicum virgatumL) neutral detergent fibre (NDF) significantly (P<0·05) increased PCA concentration 12·3 to 32·7 mg g−1NDF and reduced (P<0·05) NDF digestibility from 385·4 to 244·4 mg g−1NDF. Treated NDF (0, 50, 100 mg PCA g−1NDF) was sieved through screens with diminishing mesh size in order to isolate fractions with increasing surface area per unit mass. Measured PCA concentration was 50% greater in PCA‐treated fractions isolated by 0.11‐mm mesh than in fractions isolated by 0·50‐mm mesh, suggesting that esterification of PCA occurred predominantly at the surface of the particle. In addition, at the highest level of PCA treatment, digestibility of the fraction isolated from the smallest mesh sieves was 17% greater than that of the material from the largest mesh sieve. The predominant placement of PCA on the particle surface constitutes a major limitation of this technique. Other serious limitations include the potential for polymerisation of cinnamic acids with free hydroxyl groups prior to esterification to fibre, and the non‐specific placement of the ester linkages on the fibre. All three factors cause the model fibre to depart substantially from the characteri

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480102

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe cell walls of forage kale (Brassica oleraceaL cvs Maris Kestrel, Vulcan and Thousandhead) stems were separated into parenchyma and secondary xylem fractions of high and low digestibility respectively. Previous work had shown that the lignified secondary xylem cell walls were the main components of the plant indigestible to ruminants. The cell walls were subjected to in‐vitro digestion with fungal ‘cellulose’ and with rumen liquor. These two methods gave well correlated results except when secondary xylem cell walls were first delignified with chlorite, when their mean digestible organic matter in the dry matter (DOMD) was 41·9% with cellulase but 64·6% with rumen liquor. Chemical fractionation of the cellulase‐digested residues showed that all fractions of the parenchyma cell walls, except the hemicelluloses from cv Thousandhead, were of high digestibility. In the secondary xylem cell walls the α‐cellulose fraction had DOMD about 50%, the pectic fraction being more digestible and the hemicelluloses less digestible: but no one polysaccharide fraction in these cell walls was completely digested or untouched

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480103

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractPea (Pisum sativumL) trypsin inhibitor, known to be a mixture of at least eight different peptides exhibiting different charges as shown by electrophoresis, was subjected to an immunochemical analysis. By PAGE‐SDS analysis, only one large diffuse band was detected showing that pea trypsin inhibitor peptides have a molecular weight between 12000 and 15000 amu. After preparative non‐denaturing electrophoresis, four major bands, as judged by Coomassie blue staining, were purified and each of them was used to raise specific antibodies in rabbits. By ELISA test, immunoelectrophoresis and absorption on an immunoaffinity column, it was shown that each antiserum directed against any one of the four bands completely cross‐reacted against each other. Thus, it can be concluded that each component of the pea trypsin inhibitor should exhibit a very strong sequence hom

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480104

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe kernel composition, lipid classes, fatty acid composition, fatty acid distribution on triglycerides and triglyceride composition of kernel fat fromAstrocaryum vulgareMart palms grown in Nigeria have been studied. Kernels had a high fat content. Lauric acid was the predominant fatty acid in the whole fat and was also the major fatty acid in the triglycerides and in the 2‐monoglycerides derived from them by pancreatic lipase hydrolysis. All the fatty acids exhibited a preference for the 1‐and‐3, positions of triglycerides, except for lauric which showed a preference for the 2‐position and oleic which exhibited a random distribution. The trisaturated triglycerides were the predominant triglyceride type and the fatty acid composition of the various triglycerides suggested an absence of completely unsaturated trigly

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480105

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe biological availability of free and protein‐bound methionine sulphoxide (MSO) was examined in nine growth experiments with chickens. The source of protein‐bound MSO was fish meals oxidised with hydrogen peroxide.Bound MSO in oxidised fish meals was equally well utilised by the chicken as was bound methionine in unoxidised fish meals when the meals were the sole protein sources in the diet. When used as supplements to a low‐methionine diet, oxidised fish meals were slightly less well utilised thanL‐methionine and unoxidised meals at the highest supplementation levels. At a low level there was no difference. FreeL‐MSO was less well utilised than freeL‐methionine when added to a soya bean meal diet and when used in purified diets. In the latter cystine was found to improve the utilisation of MSO.High levels of MSO were found in muscle extracts of chickens even when no MSO was present in

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480106

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractVanillin is probably the most widely used flavouring agent for sweet foods such as biscuits, desserts, ice cream etc. It has been argued, however, that vanillin is used not only as a flavouring ingredient but also to mask undesirable off‐flavours developed during storage by products susceptible to oxidative degradation.This paper shows that vanillin not only adds its pleasant flavour note, but also acts as an antioxidant in complex foods containing polyunsaturated fatty acids. It is shown that the keeping quality of precooked dried cereal flakes was considerably increased by the addition of 0·01–0·5% (on a dry matter basis) of van

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480107

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA dynamic headspace analysis is employed for isolating aroma volatiles directly from entire black truffles (Tuber melanosporum). The qualitative analysis is carried out by gas chromatography‐mass spectrometry. The formation of the major volatile compounds and their contribution to the final aroma impression is also discusse

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480108

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe appearance, texture and flavour of cooked British sausages were assessed by 11 trained panellists using their analytical profile of 19 attributes, each of which was rated on an unstructured line scale. Five independent components were isolated, accounting for 86% of the sensory variation. ‘Saltiness’ was the only independent attribute. A map of sausage quality showed that ‘skin toughness’, ‘firmness’ and ‘meatiness’ were related closely to the principal sensory axis, and ‘juiciness’ and ‘fattiness’ to the second principal axis. The attributes of appearance describing the degree of doneness, and those describing comminution in appearance and in texture, were related to both principal axes. Mapping instrumental measurements into the sensory space showed that puncture and compressive strengths and nitrogen content were the best measures of variation on the first principal axis, indicating a toughness/tenderness component influenced by lean meat content. Fat increased juiciness, but, as salt or rusk increased, sausages were drier and more cohesive. Adhesion and cohesion were assessed as ‘cohesiveness’. ‘Fattiness’ and ‘saltiness’ were related poorly to fat and salt contents, respectively. ‘Fattiness’ decreased in tough, dry sausages of low pH, and ‘saltiness’ decreased as pH, fat and ‘dryness’ increased. In commercial sausages, the effects of comminution on eat

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480109

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA method of purifying superoxide dismutase (SOD; EC 1.15.1.1), free from lipoxygenase (EC 1.13.11.12) and catalase (EC 1.11.1.6), from ethanol‐treated soya beans is described, Preparations with the highest activity were obtained from new season's beans. Although not homogeneous by electrophoretic analysis, the preparation was 300‐fold purified. The enzyme has a molecular weight of 36 300 and a subunit molecular weight of 18 000. Its sensitivity to cyanide suggests that it is a typical cupro‐zinc SOD. Isoelectric focusing showed the presence of three separate charged species with isoelectric points of pH 4·73 (the major species), 4·55 (the minor species), and 4·37. The enzyme withstands 45 min at 65°C without loss of activity, and loses only half its activity in 30 min at 75°C at pH values between 5 and 8. Severe losses in activity at pH 4 and below are observed at 75°C. The enzyme can be stabilised for storage at 4°C in 60% (v

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480110

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of finished dough temperature, fermentation time, and intermediate and final proving time on the quality of Arabic bread has been investigated. Statistical analysis of the loaf scores indicated that all these factors affect the bread quality, sometimes in several ways. Final proving time and its combined effect with dough temperature were most significant.Extension of final proving time had the advantage of producing blister‐free Arabic bread and of improving the crust smoothness, evenness of layers and crumb texture, although darker crust and crumb colour resulte

ISSN:0022-5142    

DOI:10.1002/jsfa.2740480111

出版商:John Wiley&Sons, Ltd    

年代:1989

数据来源: WILEY