EFFECT OF HIGH PRESSURE PROCESSING ON THE TEXTURE OF SELECTED FRUITS AND VEGETABLES

Prepared fruits and vegetables were subjected to high pressure processing at 100–400 MPa for 5–60 min in an isostatic press and their influence on product texture was evaluated. Pressure had a dual effect on product texture characterized by an initial loss in texture, ascribed to the instantaneous pulse action of pressure, followed by a more gradual change as a result of pressure-hold. The extent of the initial loss and the subsequent partial recovery were pressure dependent with the former more prominent at higher pressures and the latter at lower pressures. The pressure treated samples were generally brighter in color somewhat resembling the appearance of mildly heat treated samples. For all vegetables pressure treated at 100 MPa for 60 min, the initial loss in texture was totally recovered during the pressure hold yielding an overall texture firmer than that of the raw product. There was no recovery of texture during the standing period at atmospheric pressure after the pressure treatment.     

THE CHEMISTRY OF TEXTURE IN FRUITS AND VEGETABLES

This review is concerned with the chemistry of the major primary cell wall components, pectins, hemicelluloses and cellulose, under conditions found during the normal handling of fruits and vegetables. These polymeric components are considered separately, then their combined changes during maturation, storage and processing are covered. The effects of tissue conditions, pH, enzymes and salt concentrations on the rate and degree of change are discussed. A large part of the review deals with the important texture-affecting reactions of pectic materials including glycosidic hydrolysis, β-elimination type depolymerization, demethoxylation, and complex formation.     

MECHANICS OF FAILURE IN FRUITS AND VEGETABLES

An understanding of mechanical failure in fruits and vegetables is essential to the reduction of damage in processing, handling and transport operations and to the evaluation of textural characteristics of foods. This paper proposes a theory of failure for solid horticultural materials based on the classification of failure as cleavage, slip or bruising. For each of these three modes of failure, the role of intensity of loading or stress in initiating failure is described. It is shown that cleavage is a normal stress phenomenon and that slip and bruising are shear stress phenomena. The mechanical properties of horticultural produce are described in terms of cleavage strength, slip strength and bruising strength; properties which may vary with ripening and loading conditions.
A failure diagram is constructed by superimposing strength boundaries on the normal and shear stress axes of the Mohr's circles representation of the applied stress state. This novel diagram is shown to apply to selected fruits and vegetables. The model can be extended to include buckling. It is shown that horticultural materials do not fail according to one failure criterion alone, but fail, on a rising load, according to the current strength boundary first encountered by an expanding stress state. Potatoes, for example, may fail by cleavage, slip or bruising, depending on the loading conditions.     

THE STORAGE LIFE OF FRUITS AND VEGETABLES

Exponential curves have been fitted to published temperature/time/quality data for both fresh and frozen fruits and vegetables. The two constants in the exponential equation are used as measures of the relative storage life of the product and of its sensitivity to temperature change. Of these 2 constants, 1 is analogous to the “Q₁₀” value often used to express temperature sensitivity, but it is independent of actual temperature. The two constants are used to provide an index of “storability” of different fruits and vegetables and a tentative classification of produce according to this “storability” is presented. Fitting curves to temperature/time/quality data also allows prediction of the effects on storage life of fluctuating product temperatures, such as are experienced during normal transport and storage.     

植物提取物用于果蔬防腐保鲜研究进展

致腐菌是诱发果蔬采后病害,造成果蔬在货架期间和贮藏过程腐败变质的主要原因.主要从植物提取物对果蔬采后致腐菌的抑制作用,不同提取方法对致腐菌的抑制效果,提取物用于果蔬防腐保鲜效果三个方面概述了植物提取物在果蔬防腐保鲜上的研究进展.     

超高(静)压处理对果蔬理化性质的影响

超高（静）压（以下简称超高压）技术用于乳制品、果蔬汁等的报道已有很多，而超高压用于固态食品是近几年研究的新课题。综述了超高压对果蔬质构的影响。超高压可以引起果蔬变软、褐变。但是超高压比热烫对果蔬的质构影响小。     

图谱法在采后果蔬果胶分子结构研究中的进展

细胞壁中的果胶物质是维持果蔬质地的重要成分.阐明果蔬中果胶的结构及在贮藏中的变化对指导采后果蔬有重要意义.简述近年来应用较广的傅里叶变换红外光谱(FTIR)、基质辅助激光解吸电离质谱(MAlDI-MS)、核磁共振(NMR)、原子力显微镜(AFM)等图谱法的原理、优点以及它们在检测采后果蔬中果胶分子结构及变化的进展,并对果胶分子结构检测技术的发展方向进行展望.     

食品中铅镉联合毒性研究进展

综述了铅镉联合毒性的研究进展，归纳了铅镉复合暴露的表现效应，分析了产生联合毒性的可能机理，提出了进一步研究的方向和需要解决的问题。     

鲜切果蔬加工HACCP体系的应用探讨

根据HACCP原理,对鲜切果蔬加工整个生产过程中出现的质量变化进行分析,确定原料验收、产品杀菌、金属检测等6个关键控制点,制定相应的纠偏措施,并制定出HACCP工作计划表,从而提高产品质量.     

果蔬采后商品化处理要点综述

主要阐述了果蔬采后商品化处理的概念、意义和灵活性，并比较详细的介绍了采后商品化处理应着重掌握的主要技术环节。     

粥化酶及其在果蔬加工中的应用研究

研究了粥化酶的粗酶特性及其在果蔬加工中的应用，并比较了粥化酶与其它果蔬加工用酶在苹果加工中的应用效果。研究结果表明粥化酶作用的最佳条件符合果蔬加工的要求，它能够不同程度的提高果蔬的出汁率及其澄清度；与其它果蔬加工用酶相比粥化酶具有作用效果好，价格便宜的优点     

壳聚糖在鲜切果蔬保鲜中的应用

对壳聚糖特有的分子结构和良好的防腐保鲜性能及其在鲜切果蔬的应用研究进行综述,展望其应用前景.     

A SURVEY OF ARYLAMINE N-ACETYLTRANSFERASE ACTIVITY IN COMMON FRUITS AND VEGETABLES

The N-acetyltransferase activity was determined in 58 common fruits and vegetables. The assay was based on acetylation of 2-aminofluorene or p-amino-benzoic acid, followed by high pressure liquid chromatographic analysis of products and remaining nonacetylated substrate. The highest specific activities were observed in Balsam pear which contained 17.37 ± 1.45 N-acetyl aminofluorene nmole/min/mg protein and 46.27 ± 6.87 N-acetyl p-aminobenzoic acid nmole/min/mg protein. N-acetyltransferase activities within the remaining 57 foodstuffs analyzed ranged from none detected to 3.39 ± 0.72 N-acetyl aminofluorene nmole/min/mg protein and none detected to 32.45 ± 6.55 N-acetyl p-aminobenzoic acid nmole/min/mg protein. This is the first demonstration of acetyl CoA: arylamine N-acetyltransferase activity in common foodstuffs.     

果蔬酶促褐变机理及其抑制方法研究进展

酶促褐变是果蔬深加工过程中存在的一个普遍且很严重的问题.本文介绍了酶促褐变的基本原理、影响因素,并从物理、化学、生物技术等方面介绍了一些酶促褐变的抑制方法.     

切割果蔬中微生物的生物控制研究进展

综述了目前切割果蔬中微生物的生物控制，包括采用微生物竞生菌株、噬菌体以及微生物代谢产物等进行微生物的生长控制。     

乙烯利在果蔬中残留量的快速分析方法

建立一种用顶空气相色谱快速测定植物生长调节剂乙烯利在果蔬中残留量化快速分析方法.在样品中添加碱液后恒温加热,吸取顶空瓶中的上层气体,采用GC-Q柱,GC-FID检测器进行测定.该方法的检测限为0.01 mg/kg,平均回收率为86.6%,相对标准偏差为2.1%～7.0%.