Effect of storage conditions on nutritive quality of soybean

Msuya, R.A.

Effect of storage conditions on nutritive quality of soybean

Autores

Descripción

Background information Post-harvest losses present a major challenge in developing countries, accounting for approximately 35% of total food waste during the post-harvest handling stage. In Tanzania, most storage-related losses are attributed to the use of inadequate storage materials. The majority of smallholder farmers rely on non-hermetic containers, such as polypropylene bags, rather than hermetic alternatives, which have been shown to compromise grain quality. This practice poses a serious threat to the quality of legumes, including soybeans. Globally, the production and demand for soybeans have increased significantly due to their wide range of uses, particularly in animal feeds, human nutrition, and various industrial applications. However, storing soybeans in non-hermetic materials, especially under conditions of high temperature and humidity, negatively affects their nutritional quality. This study aims to investigate the effect of storage temperature and storage materials on the nutritional quality of two soybean varieties predominantly grown in Tanzania. Methodology Sun-dried samples (Uyole soya 2 and SC. SC Semeki) were collected from the Songwe region, and transported to the Food Quality Laboratory at the International Institute of Tropical Agriculture (IITA) in Dar es Salaam, Tanzania, where they were stored in a seed storage chamber for 3 months. The study investigated the effect of three experimental factors: soybean varieties (SC. Semeki and Uyole soya 2), storage material (polypropylene and Purdue Improved Crop Storage {PICS} bags), and storage temperatures (15°C and 25°C). Sampling and analysis were conducted at 30 days intervals for a period of 90 days, at i.e. 0, 30, 60, and 90 days. Protein content in the grain samples was determined using the Kjeldahl method, Amino acid profiles were analyzed using High Performance Liquid Chromatography (HPLC). Mineral composition was assessed using two techniques: Atomic Absorption Spectrophotometer (for Calcium, potassium, magnesium, manganese, iron, copper, and zinc) and UV-visible spectrophotometer for phosphorus. Functional properties were analyzed using different methods: emulsifying capacity (EC) via UV-visible spectrophotometer, oil absorption capacity (OAC) using homogenization method, and protein solubility (PS) using the Kjeldahl method. All collected data were analyzed using R studio software. Descriptive statistics were computed, and a three-way analysis of variance (ANOVA) was performed for Protein content, functional properties, amino acid profiles, and mineral composition. Regression analysis was also conducted for mineral composition. Results and Discussion Soybean varieties had a significant effect on the nutritional quality of grains and the functional properties of Soy protein isolate (SPI), with varying degrees of reduction across different quality parameters. By the end of storage period, protein content decreased more significantly in Uyole Soya 2 (9.9%) compared to SC. SC Semeki (6.8%), However, SC Semeki retained significantly higher (p<0.05) concentration of several amino acids, including histidine, alanine, arginine, proline, tyrosine, methionine and cystine. In contrast Uyole Soya 2 exhibited significantly higher concentrations of aspartic acid, glycine, isoleucine and leucine. Regarding SPI functional properties, SC Semeki showed greater increase in emulsifying capacity (EC) and oil absorption capacity (OAC) by 31% and 25% respectively, compared to Uyole Soya 2 by 29% and 17.7%. On the other hand, the mineral content decreased more sharply (up to in SC. SC Semeki (up to 49%) than in Uyole Soya 2 (up to 38%). These differences in nutritional quality are likely due to genetic variations, which affects each varieties sensitivity to storage conditions. Storage conditions, specifically storage materials and temperature, had notable on grain quality. Storage in polypropylene bags at 25°C resulted in the greatest deterioration, including a 12% reduction in protein content and up to 41% loss in mineral composition. In contrast, PICS bags at 15°C preserved nutritional quality more effectively. Twelve out of seventeen amino acids were better retained in PICS bags compared to polypropylene, and 6 of 17 amino acids showed higher concentration at 15°C than 25°C. In terms of SPI functional properties, polypropylene storage at higher temperatures led to a 14% decrease in Protein Solubility (PS), while EC and OAC increased by 40% and 28% respectively. These changes can be contributed to the lack of controlled conditions in non-hermetic materials, which expose grains to fluctuations in moisture, air exchange, temperature, and relative humidity. Such conditions accelerate biochemical reactions that lead degrade nutritional quality. Conclusion and Recommendation The findings support the use of hermetic storage materials (such as PICS bags) and lower temperature storage to maintain the nutritional quality of grains. These results underscore the importance of encouraging agricultural stakeholders, including farmers, extension agents, and policy makers to adopt these improved postharvest practices. Future research should explore effect of storage on a wider range of soybean varieties and under diverse geographical and climatical conditions. Additionally, further studies should investigate the long-term impacts of storage duration, and the underlying biochemical mechanisms affecting nutrient retention. This will help to guide the development of more effective and targeted preservation strategies.