P1-07 Impact of Moisture Content and Temperature during Rice Storage on Levels of Mold and Aerobic Bacteria over Time

Monday, July 10, 2017
Exhibit Hall (Tampa Convention Center)
Kristen Gibson , University of Arkansas , Fayetteville , AR
Giselle Almeida , University of Arkansas , Fayetteville , AR
Wenjun Deng , University of Arkansas , Fayetteville , AR
Bhagwati Prakash , University of Arkansas , Fayetteville , AR
Shweta Kumari , University of Arkansas , Fayetteville , AR
Terry Siebenmorgen , University of Arkansas , Fayetteville , AR
Introduction: Rice (Oryza sativa) in the Mid-South United States is typically stored at 11 to 13% (wet basis) moisture content (MC). Lacking standard practices, some rice is over-dried resulting in lower rough rice (RR) mass and higher drying costs. Conversely, under-drying could favor microbial growth (mold, aerobic bacteria) and cause quality reductions.

Purpose: This study aims to determine the impact of storage MC and temperature on concentrations of mold and aerobic plate count (APC) in RR stored over a 12-month period.

Methods: Long-grain rice (cultivar Roy J) was harvested at three locations from Northern to Southern Arkansas. Composite samples were divided, dried to 12, 13, 14, or 15% MC, and stored at 25 or 35°C for up to 12 months. To determine total mold and APC at harvest, after drying, and at specified storage durations, both surface elution (SE; hand massage) and total elution (TE; stomacher) methods were applied to duplicate 25 g RR samples. Eluents were collected, diluted, and plated on 3M Petrifilm for Mold/Yeast and APC and incubated per the manufacturer’s instructions.

Results: Analyses have been completed through two months of storage. Total elution yielded ~0.47 and ~0.94 log CFU/ml greater mold and APC counts, compared to SE. Regardless of the MC level, storage at 35°C yielded significantly (P≤0.015) lower mean log CFU/ml mold (3.28±0.66) and APC (5.73±0.59) compared to 25°C with 4.43±0.35 and 6.75±0.44 log CFU/ml mold and APC, respectively. Overall, the higher MC levels of RR stored at 35°C yielded lower microbial concentrations for all harvest locations compared to 12%. Analysis of ≥4 months storage is ongoing.

Significance: Determination of optimal storage conditions for rice is imperative to decrease potential food safety issues (toxigenic molds) and quality issues (color, milleability, milling yields). Additionally, less energy intensive practices related to drying could increase sustainability within the rice industry.