Effects of modified atmospheres on textural and cell wall changes of asparagus during shelf-life.
Everson, H. P.; Waldron, K. W.; Geeson, J. D.; Browne, K. M.;
International Journal of Food Science & Technology Year: 1992 Vol: 27 Issue: 2 Pages: 187-199 Ref: 29 ref.
1992
บทคัดย่อ
Green asparagus spears (cv. Regal) harvested on 16 May, 30 May and 6 June 1989 were packed in rigid PVC trays (300 g/pack) over-wrapped with non-perforated 15 micro PVC stretch film (Auto RMF-A), with a similar microperforated film or with a highly perforated control film. Packs were held at 8 deg C for 1 d, then transferred to 20 deg to simulate commercial cool chain distribution and ambient display. Respiration rates as mg CO2 production kg-1 h-1 were determined for each harvest, and changes in the pack atmosphere composition and weight losses were monitored during shelf-life. On the day of harvest, and after 3 and 6 d of shelf-life, shear forces required to cut through spears and visual quality were determined, and cooked samples were assessed for tenderness, stringiness, flavour and bitterness by a trained sensory panel. At these intervals, samples of spears from each treatment were also extracted for alcohol-insoluble residues, from which the composition of sugars and cell wall phenolics were also determined. Rates of respiration and the extent of pack atmosphere modification were similar for each harvest; in non-perforated packs, CO2 increased to >11% and O2 fell to <2%, whereas in microperforated packs, CO2 equilibrated to 5-6% and O2 decreased to a minimum of 6-7%. Minimal changes were observed in control packs, where CO2 remained < 2% and O2 remained >18% throughout shelf-life. The shear forces needed to cut stems increased during 6 d shelf-life; this increase was greatest for control-packed spears and least for those from non-perforated packs. Regrowth (elongation of the stem and opening of bracts) was almost eliminated in non-perforated packs, and much reduced in microperforated packs, compared with control packs. Spears in microperforated packs became slightly less tender and more stringy, whereas control-packed spears became much tougher and stringier during shelf-life; changes in flavour and bitterness were slight. Spears from the second and third harvests in non-perforated packs developed a high incidence of soft rot (73 and 100%, respectively) caused by Erwinia carotovora after 6 d shelf-life. Levels of most cell wall-sugars changed little, although some obvious changes were detected during shelf-life; galactose decreased in all treatments, and arabinose decreased and xylose content increased considerably (67%) in control-packed spears. Similarly, spear lignin content increased by >400% in control, by 200% in microperforated and by <100% in non-perforated packs. The relationships between instrumental and sensory methods for assessing textural changes in asparagus and the changes in cell wall composition, and the effects of modified pack atmospheres on these changes are discussed. The possible benefits and limitations of modified atmosphere packaging to retard postharvest deterioration, particularly textural changes in asparagus are also discussed.