Dry Matter Loss and Lipid Oxidation Evaluation of Soybeans During Storage at Elevated Temperatures and Moisture Content

Abstract

HighlightsRates of dry matter loss and lipid oxidation increased as moisture content and temperature increased.Temperature effects were smaller than moisture content effects.Sums of hexanal and 1-hexanol concentrations were used as lipid oxidation indicators during storage.Lipid oxidation products were correlated positively with dry matter loss (r = 0.88) and dry matter loss rates (r = 0.84).Abstract. After harvest, soybeans are susceptible to physical, chemical, and biological changes. Prolonged storage under unfavorable conditions, such as elevated temperature and moisture content (m.c.), is responsible for accelerating dry matter loss (DML) rates and lipid oxidation (LO). Knowledge of DML rates (vDML) is useful in developing maximum allowable storage time (MAST) guidelines for soybeans. In addition to DML, monitoring changes in the lipid fraction is essential to assess quality since soybeans are valued for their oil content. The objective of this study was to estimate DML and LO of soybeans during a 30-d period over a wide range of m.c. (14% to 22%wb m.c.) and temperature (25 to 35°C), which were chosen based on climate conditions from low latitude regions where major soybean producing countries are located. A series of respiration tests were conducted using a static grain respiration measurement system with a sensor unit to monitor carbon dioxide (CO2) concentration, which was used to estimate DML. After each respiration test, samples were collected for chemical analysis. Headspace-solid phase microextraction gas chromatography-mass spectrometry was employed to determine volatile compound concentrations, which served as LO indicators. Moreover, volatile compound analysis was also used to evaluate the formation of anaerobic respiration products and other compounds that can affect soybean quality during storage. There was an increase in vDML with increased m.c. and temperature. Across the temperature range chosen, vDML increased 40 to 46 times for soybeans at 18%wb m.c. compared to 14%wb m.c. and 2.7 to 3.7 times for soybeans at 22%wb m.c. compared to 18%wb m.c. Temperature effects on vDML were smaller than moisture effects. vDML increased 1.1 to 3.5 times across the temperature range tested at constant moisture. Changes in storage conditions also affected the formation of volatile compounds. The sum of hexanal and 1-hexanol concentrations (ppm), used as LO indicators, was higher in samples with elevated m.c. Concentrations of these compounds increased 1.3 to 5 times for 22%wb soybeans compared to 18%wb m.c. and 4.6 to 11.8 times for samples at 18%wb compared to 14%wb m.c. at the same temperature. LO products were positively correlated with DML (r = 0.88) and vDML (r = 0.84); this confirmed that lipids are degraded in addition to DML when soybeans are subjected to unfavorable storage conditions. This correlation can be useful to improve MAST guidelines based on qualitative and quantitative deterioration. Keywords: Dry matter loss, Grain storage, Lipid oxidation, Respiration, Soybeans, Volatile compounds.