The accuracy of predicting dry matter digestibility of grasses from lignin analysis by three different methods

The lignin content of 50 samples of five grasses of known in vivo digestibility were determined by the methods of van Soest and Wine,¹ and of Edwards² which utilise the solubility of lignin in potassium permanganate and in HCl-activated trigol, respectively, and of Christian³ in which the sample is refluxed with acid detergent after treatment with 72% sulphuric acid without any preliminary extraction. Mean lignin values for the three methods were 4.97, 5.57 and 7.24 and the errors in predicting dry matter digestibility were ±3.9, ±4.5 and ±2.4, respectively. When compared with the error of ±2.1 previously obtained on the same samples with the in vitro technique of Tilley and Terry⁴ only the method of Christian³ appeared favourable.     

BOOK REVIEWS

Book reviewed in this article:
Glucose Syrups: Science and Technology , Edited by S. Z. Dziedzic and M. W. Kearsley.
Starch Conversion Technology . Edited by G. M. A. van Beynum and J. A. Roels.
Analysis of Food Carbohydrate . Edited by G. G. Birch.
Developments in Dairy Chemistry-2 , Lipids. Edited by P. F. Fox.
New Frontiers in Food Microstructure . Edited by D. B. Bechtel.
Methods for the Determination of Vitamins in Food . G. Brubacher, W. Muller-Mulot and D. A. T. Southgate, Eds.     

Measuring Dietary Fiber in Human Foods

Compositions of neutral detergent fiber (NDF) residues and water insoluble fiber fractions extracted by the Southgate method from five foods were determined quantitatively and compared. Neutral saccharide compositions of the two fiber residues, measured by HPLC, were similar for four of the five foods. Uranic acids constituted 4 - 8% of fiber in all foods. When adjustments were made for protein, starch and moisture contents, mean recovery of the two fibers was 97.9 f 3.9%. Gravimetric quantitation of NDF or of a Southgate-derived insoluble fiber usually yielded a fiber content similar to the chemically determined value, although each of the Southgate residues had to be corrected for starch and/or crude protein content.     

A rapid method for determining the carbohydrate component of dietary fibre

A simplified procedure for the determination of the non-starch polysaccharides in foods is described. Starch is removed by treatment with heat-stable α-amylase and resistant starch by treating with dimethyl sulphoxide (DMSO) and amyloglucosidase. Total neutral sugars and uronic acids are then measured colorimetrically in the acid hydrolysates of the starch-free material.The method is more rapid than the complex fractionation procedures (Southgate, 1969; Selvendran et al., 1979; Englyst, 1981) but does not provide a detailed composition. The time per sample compares favourably with the gravimetric assay of Asp et al. (1983) and a direct measure of the carbohydrate content of the dietary fibre fraction is obtained. The results compare favourably with those obtained by the complex method of Englyst et al. (1982). The method is applicable to a range of foods, both raw and cooked, and should have application in the routine analysis of dietary fibre since it is comparatively rapid and does not require complex or expensive equipment.     

Rapid method for the simultaneous GC quantitation of acids and sugars in fruits and vegetables.

Rapid methods of analysis for the simultaneous determination of acids and sugars in fruits and vegetables using trimethylsilylation and gas chromatography are reported. The methods have been shown to be generally applicable, rapid, simple and cheap. Typical applications are shown involving the determination of a range of organic acids and sugars in carrot, potato, cucumber, tomato, apple, pear, grape, strawberry and citrus fruits.     

Application of Van Soest Acid Detergent Fiber Method for Analysis of Shellfish Chitin

The Van Soest acid detergent fiber method was compared with the modified Welinder method for chitin analysis of Alaskan crab and shrimp meals to determine whether chitin constituted a significant fibrous component of shellfish meals. In the Welinder method, chitin is determined gravimetrically following decalcification and deproteinization with .1 M ethylenediaminetetraacetic acid and 2 N sodium hydroxide, respectively, Chitin is a fibrous component of shellfish meals, and the Van Soest acid detergent fiber method is acceptable for determination of shellfish chitin.     

Rapid Enzymatic Assay for Ascorbic Acid in Various Foods Using Peroxidase

Based on direct spectrophotometry and the oxidation of ascorbic acid by guaiacol peroxidase, this method was simple, rapid and highly specific for ascorbic acid. No interference was seen for any food sample tested, including vegetables, fruits, potatoes, beans, chicken liver, processed food, tea and seaweed. This method was applicable to colored and/or sugar-rich samples, and more precise than officially adopted chemical methods.     

生物保鲜剂在果蔬保鲜中的应用研究进展

生物保鲜剂具有天然、无毒等特点,越来越受到人们的青睐,在果蔬保鲜中有着广阔应用前景。本研究概述了生物保鲜剂的定义与保鲜机理,然后从植物类、动物类、微生物类和酶类这4个方面详细阐述生物保鲜剂用于果蔬保鲜的国内外研究现状,分析了生物保鲜剂在果蔬保鲜发展中存在的问题,并对其应用前景进行展望,旨在为生物保鲜剂在果蔬保鲜应用的深入研究提供参考。     

Total nitrogen vs. amino-acid profile as indicator of protein content of beef

In most cited food composition studies and tables, the proximate system measures protein as total nitrogen (N) (determined by Kjeldahl or Dumas method) multiplied by a specific factor. A factor of 6.25 is used for determining total protein from total N (Jones, Munsey, & Walker, 1942). Although more expensive, it is considered more accurate to base protein content of foods on amino acid data (Greenfield & Southgate, 2003).     

枸杞子掺伪检测方法的研究进展

枸杞子以其药用价值和营养品质深受消费者的青睐,广泛应用于食品和保健品行业。但是市场上枸杞子恶意掺杂、掺假现象日益严重,此行为严重影响枸杞子品质、危害消费者健康、损害消费者权益、扰乱市场正常秩序,如何正确鉴别枸杞子真伪成为广大消费者普遍关注的问题。本文对枸杞子的主要掺伪现象进行了综述,并介绍了性状鉴别、显微鉴别、化学成分分析鉴别、分子生物学技术鉴别和基于红外光谱、近红外光谱和拉曼光谱法、机器视觉和电子舌等技术的快速检测方法在枸杞子品种和产地掺伪检测中的应用情况,对不同检测方法的优缺点进行对比分析。通过对枸杞子掺伪主要检测方法的比较,为市场监督枸杞子的品质提供理论基础和研究依据。     

Simplified methods for the preparation and analysis of dietary fibre

A critical study was made of the various factors which affect the quantitative removal of starch, by enzymic methods, from starch-rich products; the products examined include potatoes, potato powder, oats and rye biscuit. Disruption of product by ball-milling in aqueous ethanol, followed by gelatinisation, are essential to give maximum enzyme accessibility as shown by light microscopy and analytical studies. The enzyme preparations were checked for the presence of contaminating β-glucanase activity using suitable substrates. The recommended method for the removal of starch involves treatment with either a mixture of human salivary α-amylase and pullulanase or amyloglucosidase; the first method was found to be slightly better. Based on these studies simplified methods for the preparation of dietary fibre (DF) have been formulated. The neutral sugars released from the DF on 1m H₂SO₄- or Saeman-hydrolysis were estimated by the alditol acetate procedure, and a modified carbazole method has been used for the estimation of total uronic acid in the fibre. A set of determinations which gives an estimate of the main types of DF polymers, including the enzymically non-degradable starch of processed products, is given. Although the method is not suitable for preparing gram-quantities of relatively pure DF, it can be used for screening a range of products. Some of the problems associated with the use of Van Soest neutral detergent fibre for estimating DF content of food products are also described.     

绿豆膳食纤维的分析

对Southgate改良法分析绿豆膳食纤维过程中酶法去除淀粉效果进行了探讨,并采用该法对全绿豆及绿豆皮膳食纤维的各级多糖进行了测定分析,为进一步利用绿豆中的膳食纤维提供理论依据.     

凉果半成品的加工方式和存在的问题

凉果是热带亚热带地区比较流行的一种休闲食品。凉果半成品的加工是凉果生产中比较重要的一个环节。本文将凉果半成品的加工归类为食盐处理、亚硫酸盐处理、普通干燥处理和蒸煮打浆处理四种方式,并对每种加工方式的加工原理和工艺进行了综述,同时对其存在的问题进行了初步的分析。     

基于电子鼻技术预测草莓采后品质

为建立一种无损检测草莓品质等级的方法,分别将草莓在20 ℃（常温）和4 ℃（低温）条件下贮藏,对草莓进行感官评价,测定质量损失率和硬度以确定其品质等级,提取电子鼻响应信号并进行分析。结果显示：电子鼻传感器阵列所含的10 个传感器响应信号与草莓品质等级相关,大多数传感器与品质等级具有显著相关性。对于常温组和低温组,主成分分析都能够正确区分不同品质等级的草莓果实;通过Fisher判别建立的回归函数对草莓常温组一级、二级、腐败级品质的判别总体准确率为97.5%;对低温组一级、二级、腐败级品质的判别总体准确率为93.3%。结果说明应用电子鼻技术实时监测草莓采后贮藏和流通过程中的品质变化具有可行性。     

高效液相色谱法测定蔬菜水果中七种植物激素的残留量

建立高效液相色谱法测定果蔬中7 种植物激素残留的方法。选择10 种果蔬样品,经体积分数80% 甲醇提取后、过C18 柱净化,用带有紫外检测器的液相色谱仪测定,外标法定量。通过对该方法的精密度和加标回收实验,所有激素的添加回收率均在70.23%～98.10% 之间,回收率的变异系数在3.34%～10.12% 之间,方法的最低检出限为0.004～0.02mg/kg、最低定量限为0.01～0.1mg/kg,所建立的果蔬中植物激素残留量的测定方法满足国家标准对食品中农药残留测定的要求,可提供给相关部门用于对相关农产品、食品的质量监控。     

果胶基复合包装在果蔬保鲜中的应用

果胶是一种广泛存在于植物细胞壁中的天然高分子材料,因具有生物相容性、易修饰和改性、可降解等优点被逐渐应用于果蔬保鲜中。果胶基复合包装因其包装性能更佳、保鲜效果更好而打破了单一果胶包装在果蔬保鲜中的局限逐渐成为果蔬的主要包装方式。本文介绍了果胶的结构及成膜特性,从塑化剂、天然聚合物、生物活性物质和纳米材料四个方面阐述了果胶基复合包装制备的主要成分,并对果胶基复合薄膜和涂膜两种方式在果蔬保鲜中的应用进行了综述并提出了展望,以期为今后食品的保鲜贮藏和新型包装材料的发展提供技术借鉴。     

The oil content of avocado mesocarp

Four methods of analysing for oil content of avocados are compared (three with gravimetric measurements): (a) Soxhlet extraction with petroleum ether, (b) homogenisation with petroleum ether, (c) homogenisation with a 2:1 (by volume) choroform/methanol solution, and one with refractmetric measurement, i.e. (d) ball milling with 1-chloronaphthalene. Conditions for Soxhlet extraction were optimised. Methods (a) and (b) gave similar results which were 6-9 % lower than those of methods (c) and (d) which were similar to each other. Saponification of the residues from methods (a)-(c) confirmed that method (c) removed more oil than methods (a) and (b) but also showed that even method (c) left some residual oil in the fruit tissues. Results are interpreted in terms of glycolipids and phospholipids remaining after extraction of triglyceride storage fractions by petroleum ether. All methods used were applicable to hard (unripe) and soft (ripe) fruits.     

不同钾肥用量对“重阳红”桃果实挥发性物质的影响

为探讨钾肥对桃果实挥发性物质的影响,对陕西主栽"重阳红"桃采用放射沟施肥法进行不同用量的钾肥处理,不施钾肥的为对照,采用固相微萃取-气相色谱-质谱联用技术测定了其挥发性物质成分和含量。4种处理桃果实中共检测出82种挥发性成分,主要由醛类、酯类、醇类、烯烃类和酮类等物质构成,其中共包含了12种特征香气物质且它们的相对含量从低到高的顺序为K3(0.93 kg/株)K2(0.70 kg/株)对照(0)K1(0.47 kg/株)。此外,施钾肥提高了桃果实中醛类、烃类和酮类物质的相对含量,降低了醇类和酯类物质的相对含量。不同钾肥用量之间对桃果实的香气影响不同,施0.47 kg钾肥果实的"果香型"香气物质的相对含量最高,其中对香气含量贡献最大的为顺-3-乙酸己酯;而施0.70 kg钾肥果实的"青香型"香气的相对含量最高,但果香味相对最淡;同时,施0.47 kg和0.93 kg钾肥桃果实中均存在"花香型"香气成分,因而香气成分表现更为丰富。因此,施0.47 kg钾肥可以使桃果实的果香味浓厚且香气物质丰富。     

The Enzymatic Determination of Starch in Food,Feed and Raw Materials of the Starch Industry

An enzymatic starch determination which can be used for the analysis of starch in a very broad range of different samples is evaluated, ranging from starch in plants, feed and food to industrial applications as starch in starch. The method is based on a complete enzymatic conversion of the starch into glucose, followed by an enzymatic determination of the glucose. A statistical evaluation of the method based on the analysis of 15 different matrices is presented. The performance of the method is compared with other methods for the determination of starch. Especially the sample desintegration and solubilization in this method perform better than in other methods which appear to be applicable in just a limited number of different sample matrices. The protocol described in this paper has been tested in an interlaboratory study, involving seven laboratories and four samples. The determination can be used in routine for the analysis of about 50 samples simultaneously, it has a good repeatability, a high selectivity, and is good applicable to samples from agricultural and industrial origin.     

正交试验优化超声波辅助提取果蔬中赤霉素GA3残留量的测定条件

采用正交试验优化超声波辅助提取-固相萃取-高效液相色谱法,建立一种简便、快速、高效地提取果蔬中赤霉素(gibberellic acid,GA3)的方法。结果表明:正交试验得到的最佳条件为超声时间45 min、超声功率128 W、料液比1∶4.5(g/mL)、甲醇浓度85%,在此条件下测得赤霉素GA3提取量为285.19 mg/kg。该方法用于10种市售果蔬中赤霉素残留量的测定,加标回收率为79.36%~97.05%,相对标准偏差为2.63%~9.99%。检测结果符合农药残留分析要求,适用于多种果蔬中赤霉素残留量的检测。