M. Wootton

Comparative studies on volatile components of non-fragrant and fragrant rices

Volatile compounds (70 in all) were identified in cooked fragrant and non-fragrant rice. The most important compounds were alkanals, alk-2-enals, alka-2,4-dienals, 2-pentylfuran, 2-acetyl-1-pyrroline and 2-phenylethanol, but many other compounds were identified that contributed to the total aroma profile. Non-fragrant rice (Pelde) contained much more n-hexanal, (E)-2-heptenal, 1-octen-3-ol, n-nonanal, (E)-2-octenal, (E)-2,(E)-4-decadienal, 2-pentylfuran, 4-vinylguaiacol and 4-vinylphenol, than the fragrant rices (Basmati, Jasmine, Goolarah, YRF9). Jasmine and Goolarah had much more indole, Goolarah and YRF9 had higher amounts of 2-acetyl-1-pyrroline compared with those of Pelde, whilst Basmati had the highest amount of 2-phenylethanol and the lowest content of n-hexanal among all the rice types examined. Results of the sensory evaluation showed that YRF9 and Goolarah had the highest pandan-like aroma whilst Basmati had the highest popcorn-like aroma.

Changes in Volatile Components of Paddy, Brown and White Fragrant Rice During Storage

Paddy rice from an Australian fragrant variety, YRF9, was dehulled and milled. A total of three samples—the original paddy and the resulting brown and white rices obtained by dehulling and/or milling—were then stored for 3 months at 30°C and 84% relative humidity under atmospheric pressure, or under a vacuum of about 150 Pa. Before storage, a sample was dehulled and milled and the volatile components were isolated from the resulting white rice using a modified Likens–Nickerson simultaneous distillation–extraction unit (SDE). After storage, the paddy and brown rices were dehulled and/or milled as appropriate and the volatile components were isolated from the resulting white rices, as well as that stored in the white rice form, using the same SDE technique. Rice stored under both sets of conditions acquired a slightly musty, rancid odour, the more so for the sample stored in air. During storage in air, there was an increase in the level of total volatile compounds in all three forms of rice, which was far greater for the white rice. This increase was largely due to aldehydes and ketones commonly formed as a result of lipid oxidation processes. This indicates that, when stored in air, the fragrant aroma character was retained better in brown and paddy rice than in white rice, because the development of off-flavours was inhibited by the protective layers of bran and hull. However, during vacuum storage, total and neutral volatiles decreased in all stored rices, with acidic and basic fractions being relatively unchanged. The volatiles profile of white rice stored under reduced pressure was closer to that of the fresh rice than were those of the equivalent storage samples of either the brown or paddy rices. During storage, the content of 2-acetylpyrroline, a compound that contributes greatly to the favourable character of fragrant rices, decreased to the extent of around 40–50% no matter what the form of the rice, or the condition of storage. It is thus concluded that, while it was found possible to inhibit the development of off-flavours to some extent, no way was found to assist the preservation of the desirable flavour compound, 2-acetylpyrroline.

Effects of High-Temperature Drying on Physicochemical Properties of Various Cultivars of Rice

Abstract Three varieties of paddy rice, namely Langi and Amaroo from Australia and Chainart I from Thailand, were dried from high initial moisture content of about 27% down to 13–14% wet basis using a two-stage drying system. A fluidized bed dryer reduced the moisture content down to 18%. Drying experiments were carried out at 100, 125, and 150°C. Further moisture content reduction down to 14% was achieved by shade drying. As a result of these treatments, head rice yield increased proportionally with the drying temperature. In contrast to that, the yellowness, measured by colorimeter in terms of b value, showed an opposite trend. Starch characteristics were studied by Rapid Visco Analyser (RVA), x-ray diffraction, and differential scanning calorimetry (DSC). Pasting properties were affected by the drying temperature. The peak viscosity and break down were decreasing with the increase of drying temperature in all varieties while the setback values were increasing in Langi and Amaroo only. All starch samples displayed the typical A type x-ray diffraction pattern. The apparent crystallinity determined by x-ray diffraction was reduced with increasing drying temperature. The gelatinization peak shifted to higher temperature while the endothermic enthalpy of gelatinization decreased with increasing drying temperature.

Sensory Testing of Australian Fragrant, Imported Fragrant, and Non-fragrant Rice Aroma

Abstract A large consumer panel of mixed age, genders, and cultural background participated in a series of triangle tests involving the aroma of rice samples obtained from retail outlets. The group could, as a whole, distinguish between Australian fragrant (AF) and non-fragrant (NF) rice and between AF and imported fragrant (IF) rices based on aroma. The ability to discriminate between the samples varied with age, gender, and cultural background. In addition descriptions of the aromas by participants implied that the aroma of AF rice was preferable to that of both the IF and Australian NF rice. The NF rice contained approximately twice the amounts of 2-hexenal[E], nonanal, 2-pentylfuran, and 2-octenal[E], and significantly more 2-nonenal[E] and hexanal, compared to the fragrant rices. 2-Acetyl-1-pyrroline (2AP) was present in both fragrant rices but not in the NF sample. The AF rice contained twice the amount of 2-heptenal[E] and three times the amount of 2-decenal[E] and 2,4-decadienal[E,E] compared to the IF rice. The concentrations of significant aroma volatiles were linked to aroma descriptions of the rices.

Simultaneous determination of food-related amines by high-performance liquid chromatography

Abstract Ten amines found in marine foods, dimethylamine, trimethylamine, trimethylamine oxide, ammonia, urea, histamine, cadaverine, putrescine, spermine and spermidine were separated by HPLC using an ion-moderated partition column. Optimum resolution and sensitivity were obtained using 0.003N sodium hydroxide as the mobile phase and UV detection at 208 nm.

Differences in Gelatinisation Behaviour Between Starches from Australian Wheat Cultivars

The gelatinisation behaviour of starches isolated from 16 Australian wheat cultivars with a wide range of pasting properties was studied using the Viscoamylograph (VAG), Rapid Viscoanalyser (RVA) and Differential Scanning Calorimetry (DSC). VAG and RVA characteristics varied between cultivars as did the enthalpy and temperatures of gelatinisation, as measured by DSC. Significant correlations existed between RVA and VAG values for maximum viscosity and breakdown. The enthalpy of the amylose/lipid complex transition, measured by DSC, was significantly correlated with each of maximum paste viscosity, breakdown, setback and viscosity at 50 °C as measured by VAG, and maximum viscosity and breakdown as measured by RVA. Starch properties that significantly correlated to gelatinisation behaviour included amylose content and the proportion of small starch granules, which had a negative relationship with VAG data for maximum viscosity, breakdown and viscosity at 50°C. Similar correlations existed for RVA data except for setback. Amylose content was also significantly correlated with the enthalpy of the amylose/lipid complex transition.

Effects of starch type and preparation conditions on substituent distribution in hydroxypropyl starches

Hydroxypropyl derivatives of wheat, pre-gelatinized wheat, maize, waxy maize and high amylose maize starches were prepared, and their acid hydrolysates analysed by high-performance liquid chromatography. Molar substitution values obtained from HPLC data were similar to those obtained spectrophotometrically except for the high amylose maize derivative, which yielded a higher value by HPLC. Substituent distribution between C-2 and C-6 was the same for both raw and pre-gelatinized wheat starches and at two different molar substitutions for the latter. This parameter was similar for all three maize starches irrespective of amylose content, but substitution at C-6 was approximately half that found for wheat starch. Higher alkali concentration during derivatization of pre-gelatinized wheat starch resulted in increased substitution at C-6.

Sensory Perceptions by Koreans of Dry‐Salted Wheat Noodles

A consumer preference study on dry-salted noodles prepared from ten diverse types of Australian wheat was conducted in Korea and Australia using a commercial Korean noodle as a control sample. Two independent panels in Korea were similar in their discriminatory responses to individual samples indicating a well-defined preference for noodle quality. Evaluation with Koreans resident in Australia for less than 2 years showed a similar preference trend to the indigenous Koreans, but Koreans resident in Australia for 7 years showed a reversed preference pattern. Data from panels in Australian noodle research laboratories also showed a similar preference pattern to the long-term Korean residents. Thus, it appears that Koreans and Australians have different taste preferences for dry-salted noodles and that Koreans resident in Australia gradually change their taste sensitivities to resemble Australian preferences.

Changes of Chemical and Physical Quality Attributes of Macadamia Nuts during Hybrid Drying and Processing

Macadamia nuts are well known for their unique flavor and taste. They contain a high level of monounsaturated fatty acids such as oleic acid, which is claimed to have an effect on reducing blood cholesterol. This study focuses on monitoring the changes in the physical and chemical qualities of macadamia nuts during drying, roasting, and storage. A combination of heat pump drying and tunnel drying was selected for this study to provide a comparison with convectional hot air drying. After completion of all drying treatments, the dried nuts were subjected to roasting at 125°C for 20 min and storage in ethylene vinyl alcohol copolymer (EVOH) bags at 4°C for 3 months. After each stage of processing, nut samples were taken to assess the quality in terms of fatty acids, moisture content, water activity, peroxide value, free fatty acids, color, and volatile compounds. The experimental results showed that drying treatments using heat pump combined with tunnel drying can reduce drying time significantly. It appears that the combination of heat pump and tunnel drying resulted in maintaining the commercially accepted chemical and physical quality characteristics of macadamia nuts in terms of key fatty acid contents, peroxide value, free fatty acid content, and color. Moreover, drying with a heat pump dryer combined with tunnel drying did not increase the content of undesirable volatile compounds in dried macadamia nuts after processing.

Correlations between objective quality parameters and Korean sensory perceptions of dry salted wheat noodles

Abstract A range of objective quality parameters from 10 diverse Australian wheats were evaluated for their relationship with previously reported data on sensory evaluation by Korean consumers of white salted noodles made from the wheats. These parameters were protein content, Falling Number and hardness for the wheats, protein content, Amylograph peak height, swelling power and Minolta colour for the flours, colour and cooking time for the dry noodle, and Minolta colour and texture measured by cutting force for the cooked noodle. For colour, significant correlations with Korean consumer preference were an inverse relationship with cooked noodle L∗ value but a direct relationship with flour L∗ value, and an inverse relationship with flour b∗ value. There was also a significant negative correlation between Korean consumer preferences and cutting force. The results suggest that Korean consumers prefer noodles made from white flour and with soft texture when cooked. Contrary to current views, no significant ...