Additive, rice volatile

In most cases, SPME is readily amenable for use in qualitative analysis. However, initial efforts to use SPME to measure rice volatiles proved less than satisfactory (20). The limitation was that the initial stationary phases used as coatings for SPME fibers were limited to temperatures slightly above ambient. Placing the fiber in the effluent (dynamic SPME) of a sample purged with nitrogen improved the recovery of volatile compounds. However, quantitation was problematic because the additional variables of purge flow rate, path, and time contributed to increased variance. 

The effect of the rice volatiles additive on toxic bait consumption was then evaluated (110). Two groups of rats were given a choice between either 0.2 zinc phophide treated rice and untreated rice, or 0.2% zinc phosphide treated rice with the rice volatiles added and untreated rice. This latter group showed almost double the toxic rice bait consumption and a mortality of... 

Dupuy and coworkers have reported a direct gas chromatographic procedure for the examination of volatiles in vegetable oils (11). peanuts and peanut butters (12, 13), and rice and com products (14). When the procedure was appTTed to the analysis of flavor-scored samples, the instrumental data correlated well with sensory data (15, 16, 17), showing that food flavor can be measured by instrvmental means. Our present report provides additional evidence that the direct gas chromatographic method, when coupled with mass spectrometry for the identification of the compounds, can supply valid information about the flavor quality of certain food products. Such information can then be used to understand the mechanisms that affect flavor quality. Experimental Procedures... 

The pH of Aji no susu is within the range of 3.9. 3, with main organic acid as lactic acid (3.1-8.6g/l(X)g). In addition, volatile short-chain fatty acids, such as acetic acid (0. l-0.6g/100g), were detected. The highly concentrated lactic acid is characteristic of Narezushi that rich in rice (carbohydrate). The concentration of lactic acid in the Narezushi (Aji no susu) made from horse mackerel and fermented for 1 year was higher than that in Funazushi and Saba (mackerel) narezushi made in Fukui Prefecture. Butyric acid and propionic acid, which are considered the main causative factors for the characteristic odour of Funazushi and Kusaya, were hardly detected. 

Unfortunately, one of the pathways of dissipation of molinate is by volatilization from the paddy water, so t t air quality remains a concern. The diurnal pattern of molinate flux from a treated paddy heavily instrumented with air sanq)lers and meteorological devices showed significant flux to the air still occurred on the 7 day after application, with about the same intensity as on the first and second days. At least half of the molinate dissipation is by volatilization, the other half by hydrolysis and other breakdown mechanisms. Air sampling conducted in the small towns in and around the rice growing region in the Sacramento Valley confirmed the presence of molinate 43). Since molinate has potential adverse reproductive effects along with its eerie sweet odor, this has been a point of contention in California, and will require additional work. 

The introduction of SPME fibers with the capability of operating at higher temperatures has resulted in improved collection of volatile compounds from the headspace of rice. Compounds not observed at room temperature can now be desorbed, collected, and concentrated in a single step. Additionally, heating the sample shifts the concentration equilibrium toward the gas phase, thus enhancing sensitivity. 

The volatile profile changes dramatically when comparing white rice and rice flour. In the rice flour, a large increase is observed in lipid oxidation products such as hexanal. An increase is also observed in the abundance of 2-AP, even though no water is added. However, the amount of 2-AP released from rice flour is similar to that from milled rice kernels when 100 pi of water is added. Addition of water to the rice flour results in no significant increase in 2-AP while reducing the amount of hexanal recovered. 

This chapter describes the application of SPME to develop a rapid, sensitive analytical technique for analyzing the volatile compounds found in the headspace of rice. A key requirement of this methodology is the heating of the sample in order to produce sufficient amounts of analytes to be successfully analyzed. Analysis of less than 1-g samples of milled or brown rice kernels is possible. The key odorant in fragrant rice is 2-AP, and recoveries are enhanced by the addition of water. However, the recovery of other compounds may be suppressed by the addition of water, as observed with the internal standard TMP. This method is readily amenable for the analysis of additional compounds once they have been identified as having an impact on the sensory quality of rice. 

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