Impact of Storage of Freshly Harvested Paddy Rice on Milled White Rice Flavor

Abstract

Between harvest and the start of drying, paddy rice may be held for more than 24 hr at moisture contents ranging from 16% to >26%. Microbes found on the freshly harvested rice grow under these conditions and produce a wide variety of volatile compounds that impact the flavor/aroma of the white rice obtained after drying and milling of the paddy rice. The contents of 10 volatile microbial metabolites were compared in white rice obtained from paddy rice harvested at differing moisture contents and immediately dried (0 hr) or held for 48 hr before drying. No increases in volatile microbial metabolite levels were observed in white rice obtained from paddy rice that was stored at 17–21% moisture contents for 48 hr. In white rice from paddy rice stored at ≥24% moisture content, 3‐methyl‐butanol, 2‐methyl‐butanol, acetic acid, 2,3‐ butandiol, and ethyl hexadecanoate increased markedly with time. Also in these samples, as determined by a descriptive panel, sour/silage and alfalfa/grassy/green bean flavors significantly increased (P < 0.1) in intensity. Sour/silage, the predominant off‐flavor note in the stored samples, correlated highly (r = 0.98) with 2,3‐butandiol. Ethanol concentration measurements on the paddy rice correlated highly with sour/silage (r = 0.99) and 2,3‐butandiol (r = 0.97), and correlated well with several other volatile microbial metabolites. Carbon dioxide measurements taken on the paddy rice did not correlate as highly (r =.78) with sour/silage. Measurements of ethanol produced in paddy rice may serve as an indicator of off‐flavor/aroma development in the resultant white rice.

Important Sensory Properties Differentiating Premium Rice Varieties

“…The other second best variety from Brazil, BRS Jaçanã, only differed from BR IRGA-417 (also harvested in 2008) by having a lower level of sour/silage (Table 4). Sour/silage is an off-flavor note that increases with increase in harvest moisture content of paddy and length of storage prior to drying (Champagne et al 2004a) and, thus, was not inherently higher in BR IRGA-417.…”

“…The technique has been used extensively for determining the effect of different growing and/or processing conditions on sensory properties of rice (Champagne et al 1997(Champagne et al , 2004a(Champagne et al , b, 2007(Champagne et al , 2009Meullenet et al 1999Meullenet et al , 2000.…”

Analysis of flavor volatiles of glutinous rice during cooking by combined gas chromatography–mass spectrometry with modified headspace solid-phase microextraction method

“…This technique was introduced in studies on the flavor indicators of rice (Grimm et al, 2001(Grimm et al, , 2004Wongpornchai et al, 2004). Champagne et al (2004Champagne et al ( , 2005 investigated the volatile microbial metabolites gathered in rice based on the SPME technique. Laguerre et al (2007) reported the rapid evaluation of rice aroma by analysis of the volatile fraction using SPME directly coupled with mass spectrometry (MS).…”

Analysis of flavor volatiles of some Iranian rice cultivars by optimized static headspace gas chromatography–mass spectrometry

“…However, the solvent extraction method is timeconsuming, as it requires many steps in sample preparation and, thus, is not appropriate when a large number of the limited amount of rice samples is to be analyzed. Champagne et al investigated the volatile microbial metabolites gathered in rice based on the solid phase micro-extraction (SPME) technique [11,12]. Moreover, Laguerre et al reported the rapid evaluation of rice aroma by analysis of the volatile fraction using SPME directly coupled with mass spectrometry (MS) [13].…”