Chemical and biochemical changes during microwave treatment of wheat

Abstract

Currently attention is paid to a possible use of microwave (MW) heating for the drying of cereal grain, rice or pulses. Heat from the kernel surface is transferred by conduction to the inner endosperm if the usual convention drying of grain with hot air is used. This method of drying is time consuming with low economic effectiveness since heat conductivity of wheat kernel is rather low, similarly to insulating materials. MW heating allows drying grains to a permitted limit moisture without deteriorating effects on its composition or properties (CAMPANA et al. 1986). MACARTHUR and D'APPOLONIA (1982) studied the influence of MW heating and grain moisture on wheat conditioning prior to milling and optimisation of semolina yield as well. Some deteriorating changes can occur as a result of high doses of MW treatment. MATERIALS AND METHODSTechnique of microwave treatment: Parameters of a MW oven Whirlpool MT 243/UKM 347 (Norrköpping, Sweden) were as follows: frequency 2450 MHz, pulsed variable MW rated values of power output -90, 160, 350, 500, 750, 850 and 1000 W, inner space volume 25.4 l, without sample rotation during measurement. Before the samples are treated, pre-heating of the oven has to be done to achieve a heating process standard. For this purpose a volume 2 l of water was heated in the oven, using a maximum power output for 5 min. The absorbed power according to BSEN 60705 test (International Standard BSEN 60705 -Methods for measuring the performance of microwave ovens for household and similar purposes) was determined every day as well. Load of water for this test is 350 ± 5 g, initial water temperature 10 ± 2°C. The mean value of absorbed power (n = 22) corresponding to the rated power output 350 W was 298.42 W; standard deviation 8.5 and coefficient of variation (relative standard deviation) 2.85% (SKULINOVÁ et al. 2002).A special polyethylene container with bottom dimensions 100 × 150 mm was used for MW treatment. Weight of single sample was 200 g, height of sample layer in the container was 20 mm. The container with sample was put in the middle of the oven, MW power output was set and the sample let heat until the desired end temperature of heated sample was reached. Then the power output of the oven was switched out and the sample was left in the oven for 1 min more to homogenise the temperature in The effect of microwave (MW) heating on the changes in wet gluten content, Gluten Index, Falling Number and amylographic characteristics was studied in sprouted wheat grain. Different moistures of wheat in two ranges of 10-11% and 15-17% and two end temperatures of MW heated samples (60 and 80°C) were applied to wheat samples. Falling Number and Gluten Index increased with increasing absorbed energy during MW heating, whereas gluten content decreased. Amylographic maximum increased due to α-amylase inactivation progressively with increasing absorbed energy as well. The greatest relative changes occurred when the end temperature of MW heated samples 80°C and moisture 15% were used. An improvement effect on...

Effect of Microwaves on Technological and Rheological Properties of Suni-Bug (Eurygaster spp) Damaged and Undamaged Wheat Flour

“…This finding indicated that thermal denaturation of glutens in sound and damaged samples might be with different microwave times owing to having different levels of proteolytic activity in flours. The changes in WG content are similar to the findings previously reported by many authours (Doty and Baker 1977;MacArthur, 1981;Campaña et al, 1986Campaña et al, , 1993Lupano and Anón, 1987;Koksel et al, 1993;Türker and Elgün, 1998;Kaasov et al, 2002;Walde et al, 2002).…”

“…Also, these results in gluten index indicated improvement of dough elasticty and strengh due to the partial inactivation of excessive proteolytic activity from wheat bug enzyme and gluten strength development. The harsh gluten occuring by thermal process were reported by many authors (Koksel et al, 1993;Ugareiah and Hackenberger, 2001;Kaasov et al, 2002;Walde et al, 2002).…”

“…The wet gluten (WG) contents of sound and damaged Baker 1977;MacArthur 1981;Campaña et al, 1986Campaña et al, , 1993Kaasov et al, 2002;Walde et al, 2002;Vadimbal and Jayas 2007), limited information is available about the effects of microwave application on quality parameters such as some technological and rheological aspects of the flour milled from suni-damaged wheat (Sivri and Köksel 1996;Türker and Elgün 1998). Our main objective in this investigation was to examine the effects of microwave energy on some specific technological and rheological properties of flours produced from undamaged and damaged wheat by suni-bug and to describe the effects of microwave treatment on excessive proteolytic enzymes in flours.…”

“…The standard PGI values of flour samples ranged from 94-100 (good quality) and 78-95 (good quality) whereas the modified PGI of samples were 95-100 (good quality) and 49-71 (very low quality), respectively, (Perten Instruments, with higher microwave energy doses and higher end temperature of sound and damaged flour samples because of different thermal inactivation degree of amylase enzymes and probably starch damage (Aref et al, 1972;Doty and Baker, 1977;Türker and Elgün, 1998;Kaasov et al, 2002).…”

Impact of drying deep beds of rice with microwave set at 915 MHz frequency on rice microbial community responses

“…Most studies that dealt with the use of MW systems for the uses of food processing, including for rice drying and decontamination, have been laboratory-based experimentations that employed MW systems operated at 2,450 MHz frequency (Kaasova, Kadlec, Bubnik, Hubackova, & Prihoda, 2002;Kumar, 2015;Le, Songsermpong, Rumpagaporn, Suwanagul, & Wallapa, 2014;Liu, Jiaqiang, Deng, Xie, & Zhu, 2016a;Liu, Jiaqiang, Ma, & Xie, 2016b). However, there has been limited success in scaling up MW heating to dry rice with the frequency set at 2,450 MHz (Cho, Aoki, Miyatake, & Yoshizaki, 1990;Kaasova et al, 2002;Maskan, 2001;Prabhanjan, Ramaswamy, & Raghavan, 1995;Vadivambal & Jayas, 2007); this has been primarily due to the limitations on depth of penetration into the grain bed and hence occurrence of nonuniform heating across thick beds (Kumar, 2015).…”