摘要:

AbstractPolyphenol oxidase (PPO) was isolated from Yali pear (Pyrus bretschneideri R). At the end of purification by ion exchange chromatography on DEAE‐cellulose, 10.8‐fold purification was achieved. The enzyme showed activity to catechol, pyrogallol, chlorogenic acid and DL‐DOPA; of these four, chlorogenic acid was the best substrate. The optimum pH for the PPO was 7.0. PPO activity was not destroyed by heating to 30° for 30 min. The effects of various compounds as inhibitors of the reaction catalysed by the enzyme were

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570302

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractInsight into the structure and digestion of the cell‐wall matrix may be gained by studying the in‐vitro disappearance (IVD) of constituents from cell types which are contained in forage fibre. The objective of this study was to determine the IVD of neutral sugars, uronic acids, esterified phenolic acids, and lignin from parenchyma and sclerenchyma walls isolated from the plant parts of cocksfoot (Dactylis glomerata L). Cell walls were incubated in a rumen fluid‐buffer medium for 0, 12 or 96 h. The chemical composition, apparent digestion and IVD of constituents varied considerably within and between cell types. Parenchyma had higher arabinose to xylose and ferulic acid to p‐coumaric acid ratios and lower lignin concentrations than sclerenchyma. The apparent digestion of parenchyma was 240% greater at 12 h and 20% greater at 96 h than that of sclerenchyma. The IVD of cell‐wall constituents from parenchyma ranged from 12 to 80% at 12 h and 46 to 99% at 96 h. The IVD of constituents from sclerenchyma was lower than that from parenchyma, ranging from 5 to 50% at 12 h and 47 to 89% at 96 h. Across all cell types, IVD was usually greatest for ferulic acid and lowest for lignin. These findings indicate that the differential loss of constituents from fibre is due in part to differential loss of constituents from both fast and slowly digested cell types. Ferulic acid was the most uniformly removed constituent across cell types. This suggests that ferulic acid is associated with regions of the cell‐wall matrix which change little between cell types relative to structural carbohydrates and ot

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570303

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThis investigation was undertaken to study the distribution and availability of Zn in different soil fractions. The proportions of total Zn present in the soils in exchangeable, organically bound, complexed or adsorbed and residual fractions were determined by sequential extraction with CaCl2, H2O2, EDTA and HCl/HNO3, respectively. Most of the total Zn was, on average, present in the EDTA‐Zn (15.5%) and HCl/HNO3‐Zn (78%) forms. The CaCl2‐Zn and H2O2‐Zn fractions averaged 5.0 and 1.5% of the total Zn respectively. Zinc present in exchangeable (CaCl2‐Zn), organically bound (H2O2‐Zn) and complexed (EDTA‐Zn) forms was closely related to the bioavailability of Zn to maize plants grown on these soils. The residual Zn (HCl/HNO3‐Zn) was not re

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570304

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractAn 8‐month‐old cattle slurry was analysed titrimetrically and the major buffer components were found to be ammonium, bicarbonate and a solid phase of carbonates. A simulation model was developed which explained the experimental results. pH stability in response to addition of HCl, superphosphate, FeCl3, Ca(NO3)2and CaCl2in increasing levels was investigated. Upon aeration, pH rose quickly by 0.4 to 1.5 units for all additives and levels, except where HCl was added equivalently to the total alkalinity of the slurry, which then kept a stable pH of 4.2. Ammonia volatilisation in response to the addition of either HCl or CaCl2was found to decrease with increasing amount of additive, HCl being more effective than CaCl2. This confirms that the total alkalinity is an important factor regulating the potential ammonia loss from cattle slurry. Addition of HCl or CaCl2close to the total alkalinity resulted in a reduction of the potential ammonia loss to 0 and 15% of the untreated loss, respectiv

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570305

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractBiochemical and microbiological changes during the fermentation of sesame (Sesamum inducum L) oilseed cake to produce the traditional Sudanese food sigda are reported. The microflora during fermentation was dominated by a homofermentative lactic acid bacterium Streptococcus sp, though initially the yeasts Candida sp and Saccharomyces sp were also present. The main fermentation product was lactic acid, the concentration of which attained 50 g kg−1during fermentation. Acetic acid was also present at levels not exceeding 15 g kg−1. No other volatile fatty acids were formed in significant quantities. The accumulation of acids led to the pH of the mixture decreasing to 4.0 after 3 days. Dried sigda possessed a crude protein content of 440 g kg−1and retained the high sulphur amino acid content of the sesame seed cake although lysine remained the most limiting amino acid nutritionally. The sigda fermentation was quite different from that of another Sudanese fermented food kawal, prepared from Cassia obtusifolia L leaves, and was also in marked contrast to the traditional oilseed fermentations practised in West Africa with respect to both the microflora and the products of fermentation.The traditional Sudanese fermented food furundu, prepared from the seed of karkade (Hibiscus sabdariffa L). was also examined. Initial findings suggest that the furundu fermentation isi ntermediate in character between that of sigda and kawal. It yielded a product iwth a crude protein content of 270 g kg−1, the protein being of excellent nutrition value with a chemical scor

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570306

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe nutritional value of seeds of mukheit (Boscia senegalensis (Pers) Lam ex Poir) and maikah (Dobera roxburghi Planch) widely used as food in times of famine in western Sudan have been investigated. The chemical composition of each food before and after the traditional debittering process is reported. Both foods compared favourably with the local staple cereals as regards the content of soluble carbohydrate and crude protein with values of 690 and 250 g kg−1respectively for mukheit debittered by soaking in water at ambient temperature and 800 and 150 g kg−1respectively for maikah debittered by boiling in water. The nutritional quality of protein in mukheit debittered by soaking in water at ambient temperature appeared similar to that of sorghum but was markedly enhanced if debittering was performed by boiling, although the crude protein content of the food fell substantially during the latter procedure. The protein of debittered maikah had a chemical score of 85 indicating a quality superior to that of the local cereals. Maikah also represented an exceptionally rich source of calcium and contained nutritionally useful quantities of z

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570307

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe nature of carbohydrates in a difficult‐milling and an easy‐milling cultivar of red gram (Cajanus cajan L) was studied. These two cultivars of red gram were milled to obtain cotyledon, intermediate fraction and husk, and various carbohydrate fractions were isolated from them and chemically characterised. The cotyledon was rich in starch and proteins and contained a water soluble polysaccharide mainly of arabinan type. The intermediate fraction had less starch than in the cotyledon and was rich in free sugars. Arabinogalactan‐type polysaccharides were characteristic of the intermediate fraction and were gummy and hygroscopic in nature. The alkali insoluble residue in the intermediate fraction was a complex of cellulose and non‐cellulosic polysaccharides. The content of this fraction and also of the pectin was greater in the difficult‐milling cultivar. The husk was rich in non‐starchy polysaccharides and contained varying amounts of arabinose and xylose in most of the fractions. Both glucuronic acid and galacturonic acid were present in the husk, whereas the cotyledon and intermediate fraction contained galacturoni

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570308

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe rate of decomposition under anaerobic conditions of two types of beechwood sawdust in a stationary bed was examined. The first order kinetics of this process was confirmed. A formula for the yield of volatile decomposition products was established. Rate constants and parameters of their Arrhenius plot were computed from experimental data.

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570309

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fate of coliforms in Turkish soudjuk during fermentation, ripening and storage was studied. Survival was highly dependent on the pH attained during fermentation. The number of faecal coliforms and Escherichia coli increased during the first 2 days of fermentation in soudjuk made with addition of 5 g kg−1fast cure coinciding with a drop in pH to 5.8 from 6.15. Thereafter a substantial reduction in numbers of faecal coliforms and E coli occurred with further decline in pH to 5.3 after 7 days. A marked decline in the number of organisms initially present was observed within 2 days in soudjuk made with 10 g kg−1glucose; this coincided with a drop in pH to 4.5. E coli was completely inactivated in 7 days in soudjuk made with 10 g kg−1glucose. In contrast, the inactivation of E coli took 21 days in soudjuk made with 5 g kg−1fast cure. In soudjuk made with 5 g kg−1fast cure, total and faecal coliforms survived better when stored under vacuum at 4° compared with ambient pressu

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570310

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe total amount of the high molecular weight glutenin (HMWg) subunits, and the amount of the individual subunits, present in kernels of wheat (Triticum aestivum L) were studied in relation to differences in growing conditions. The amounts of individual HMWg subunits in four varieties, each grown at six sites in The Netherlands, differed considerably between the sites. Only to a limited extent (0‐66%, depending on variety) could this variation be ascribed to differences in protein content of the samples. The cause of the rest of the variation is unknown. Accordingly, the total amount of the HMWg subunits, relative to the total amount of proteins present in a wholemeal flour of a variety, differs between the samples produced at different sites. Thus the preference for synthesis of a certain protein fraction may vary depending on the environment. A second experiment showed that variation in protein contents of samples of two varieties grown on the same trial field accounted for about 90% of the variation in the total amount of HMWg subunits. The samples of each variety differed in protein content as a result of differences in the amount of N fertiliser applied. Within each variety, the ratio between the individual HMWg subunits was less dependent on variations in environmental conditions than on the actual amount, indicating that the levels of expression of the individual HMWg subunit genes are regulated by a common mechanism.The implications of the results for the selection possibilities of wheat with desired bread‐making quality and for studies concerning genetic Variation in the amount of HMWg subunits are discus

ISSN:0022-5142    

DOI:10.1002/jsfa.2740570311

出版商:John Wiley&Sons, Ltd    

年代:1991

数据来源: WILEY