No abstract

A number of factors affecting anthocyanin stability and color are discussed in this review. 13re anthocyanins are probably the most spectacular of plant pigments since they are responsible for most of the red, purple and bluepigmentation ofjlowers, h i t s and vegetables. However, because of their highly reactive nature, anthocyanins readily degrade, or react with other constituents in the media, to form colorless or brown colored compounds. lhe presence of an oxonium ion adjacent to carbon 2 makes the anthocyanins patticularly susceptible to nucleophilic attack by such compounds as sulfur dioxide, ascorbic acid, hydrogen peroxide and even water. Loss of anthocyanin pigmentation also occurs in the presence of oxygen and various enzymes, and as a result of high temperature processing. A certain degree ofpigment stabilization may be conferred by acylation with various organic acidr , copigmentation, self-association and/or metal chelation. In addition, pH has a marked effect on anthocyanin stability, and on the color of media containing these pigments. A number of anthocyanin-rich sources have been investigated for their potential as commercial pigment extracts. Although their application is primarily limited to acidic 'To whom correspondence should be directed.

No abstract

Chilling injury (CI) is a physiological defect of plants and their products that results in reduced quality and loss of product utilization following exposure to low but nonfreezing temperatures. To design more effective control strategies and maximize shelf‐life, it is necessary to develop an understanding of the biochemical mechanism(s) responsible for the initiation of CI. Despite considerable efforts in this field of study, there is no general agreement on the cause or nature of CI, or even the primary event(s) triggering low temperature damage. The first unified theory to explain CI was founded on low temperature induced membrane lipid phase transitions leading to a loss of membrane integrity and physiological dysfunction. This was modified to account for the observation that the level of certain high melting phospholipids appears to be related to the chill sensitivity of many plant tissues. Membranes and changes in their physical characteristics are further implicated as having a role in CI by the discovery that chilling stress evokes an elaborate membrane retailoring response that leads to increased fluidity at reduced temperatures. Others have postulated that CI results from the direct effect of reduced temperatures on enzymes or the indirect effect of membrane perturbations on intrinsic enzymes. The redistribution of cellular calcium has most recently been advanced as the primary transducer of CI. The weight of this theory rests on the role of calcium as a secondary messenger for many cellular functions. In this review it is also speculated that lipid peroxidation may have a role in the development of irreversible injury during low temperature stress. Its effect would be similar to the senescent processes of free radical damage to tissue and progressive membrane rigidification.

The effects of chilling on tomato (Lycopersicon esculentum Mill cv. Caruso) texture were investigated using fruit stored at 22°C (nonchilled) or 5°C (chilled) for 28 days. or at 5°C for 15 days before transfer to 22°C to facilitate ripening during and additional 13 days (prechilled). Prechilled fruit exhibited symptoms of slight chilling injury, i.e. development of mealiness, accelerated softening relative to that of nonchilled fruit and nonuniform surface colour development. The firmness of all fruit decreased during ripening and chilled storage when measured by flat plate compression and puncture, especially during the early stages of ripening of nonchilled and prechilled fruit. The compression firmness of pericarp tissue similarly decreased during ripening of nonchilled and prechilled fruit, but was maintained during chilling. Total moisture content (ca 94%) of tissue, uronide content (32‐35% w/w) and extracted β‐galactosidase activity did not differ significantly (P > 0.05) among fruit during ripening and chilled storage. The degree of uronide methyl esterification in ethanol‐insoluble solids prepared from pericarp tissue (EIS) was relatively low for all fruit. i.e. <40%. EIS from which greater levels of pectinesterase were extracted (i.e. nonchilled>chilled>prechilled) exhibited decreased levels of uronide methyl esterification. Markedly elevated levels of β‐glucosidase activity were extracted from prechilled EIS. Total polygalacturonase activity (mainly as PGI) and autolysis of enzyme‐extracted EIS were inversely correlated (P≤ 0.05) only with the loss of nonchilled fruit and tissue firmness and prechilled fruit firmness. Results suggest a possible role for β‐glucosidase in textural changes of prechilled fruit and tissue (e.g. loss of firmness, development of mealiness) and also implicate loss of skin strength in the softening of whole fruit during chilling.

Mature-green tomatoes chilled 15 days (5°C; RH >85%) were softer than nonchilled during subsequent ripening (22°C) by both whole fruit and pericarp tissue puncture @<0.05), but not by flat-plate compression. No differences in total polygalactnronase (PG) or PG isozyme activity were evident although total activity was greater in nonchilled after 10 days ripening. Softening of nonchilled fruit correlated (pcO.05) with extracted PGI activity, while chilling-associated softening correlated @<0.05) with higher initial extracted pectinmethylesterase (PME) activity. Extracted peroxidase remained constant throughout ripening but was greater @<0.05) in pre-chilled fruit consistent with chill-induced membrane dysfunction. Transmission electron microscopy showed the middle lamella from pre-chilled tomatoes was swollen and less defined. Loss of turgor from translocation of water to the PME-modified cell wall was suggested to be responsible for softening as a consequence of chilling.

ABSRACTThe various quality aspects of chilling injury (Ct) serve as the focus of this review in which symptoms, occurrence and its alleviation are discussed. CI is a term used to describe the physiological damage that occurs in many plants and plant products, particularly those of tropical and subtropical origin, as a result of their exposure to low but nonfreezing temperatures. The substantial economic consequences of CZ have provided the impetus for studying/developing effective means of alleviating symptoms which manifest this disorder. A diversity in plant responses to low temperature stress exists, including alterations in ethylene biosynthesis, increased respiration rates, cessation of protoplasmic streaming, increased solute leakage, and uncoupling of oxidative phosphorylation. These various responses ultimately give rise to an array of visual symptoms (e.g., surface pitting, water rot, poor color development, general loss of structural integrity) which can render severe losses in product quality borh pre-and postharvest. A number of different methods are available by which to alleviate symptom development, including manipulation of storage conditions (e.g. , temperature cycling, hypobaric and modijed atmosphere storage), exogenous chemical treatments (e. g. , application of phospholipids, antioxidants, calcium) and genetic modijcation of chill sensitive species. These are discussed with respect to their effectiveness and possible control mechanisms.

Methods of analysis for naturally occurring anthocyanins are described. The large number of chemical groups which may bind to the flavylium molecule has contributed to a large variation in structure, making the qualitative analysis of anthocyanins difficult. Qualitative analysis has generally involved preliminary solvent extraction followed by chromatographic separation and purification of pigments. Individual anthocyanins are then characterized by their chromatographic mobility, absorption spectra, and by means of controlled hydrolysis and oxidation tests. Quantitative analysis of anthocyanins may be carried out using either differential or subtractive spectral methods. The validity of results obtained by either of these methods is dependent on the presence or absence of interfering substances within the samples. Where the quantification of individual anthocyanins is desired, their separation from a mixture, normally by means of column chromatography, is first necessary. High resolution of microgram quantities of anthocyanin without the need for extensive sample purification prior to analysis has led to an increase in the use of HPLC techniques for quantitative work.