Keeping Quality of Green Soybeans by Whole Plant Packaging

Abstract

Green soybeans, immature seeds of Glycine max Merr., are widely used in Japan as vegetable and snack etc. Their quality, however, rapidly deteriorates after harvest. We suggested previously that the polyethylene packaging of whole plants with pods, leaves and roots, unlike such conventional shipping styles as packaging of pods with mesh bag or non-packaged bunch of plants without leaves, effectively prevents the deterioration of taste of beans and also external appearance of pods even at room temperature. In the present study, the effect of whole plant packaging (WPP) was confirmed and the various factors affecting the effect were investigated. Whole plants of`Shirayamaof`Shirayama-dadachamame' cultivar were packaged in low-density polyethylene bags of 0. 03 mm in thickness and held at 20'C as standard WPP. As control materials, pods were packaged in perforated polyethylene bags. The changes in sugar content and free amino acid index (optical density of ninhydrin positive 80 %-ethanol extracts) were used as the criteria of taste changes of beans. WPP was very effective in keeping the external quality of pods. Although control pods discolored in 4-5 days at 201C and became unsalable, those in WPP kept green more than a week. Packaging with bags of 0. 04 mm in thickness was comparable in its effect to the standard packaging with 0. 03 mm bags, but the effect of 0. 06 mm bags was slightly inferior. Pinholes were made on 0. 06 mm bags on the purpose to avoid possible excessive accumulation of CO2 and/or depletion of 02 resulting from using thick film. The effect of WPP with the pinholed bags decreased considerably in comparison with that of tight packaging, although it was evidently superior to the control. At 25C, the effect of WPP on the external appearance was also obvious including liner packaging for bulk materials. Contents of sugar and free amino acid in beans rapidly decreased within 1-2 days in control materials at 20C, but the decrease was markedly retarded by WPP. Packag ing of whole plants with perforated bags also retarded the decrease, but the effect was generally inferior to that with sealed bags. Sealing of whole plants from which the roots were cut off, or of branches with pods and leaves, showed somewhat uncertain effect as compared with sealing of complete whole plants. When all leaf blades were cut off from the plants, the effect was markedly reduced, and cutting of distal halves of every leaf blades proportionally reduced the effect. When the plants with wilted leaves were packaged, the effect of WWPI' was also markedly reduced. Packaging of whole plants with pinholed bags showed the effect to a certain extent, but was inferior to tight packaging in its effect on retarding the decrease of sugar and amino acid contents. 11982"N1OEŽ18"ú Žó-• ƒGƒ_ƒ}ƒ•ŽûŠnOEã ‚Ì •i Ž¿•Ï ‰» ‚AE ‚» ‚Ì-h Ž~('ae2•ñ)-{OE¤ ‹ † ‚ð ŽÀ Ž{‚· ‚é‚É "-‚½‚è,‰€ OE|•U‹» •¼" ‡•à 'c ‚ae‚è•• •¬‚ðŽó‚¯ ‚½. 2OE» •Ý'å •ã •{-§ 'å Šw"_Šw•" 224