Yulafa Uygulanan Hidrotermal Isıl İşlemin Yulaf Unu ve Kepeğinin Depolama Stabilitesi Üzerine Etkisi

Abstract

Compared to other grains, oats (Avena sativa L.) have a high dietary fiber, fat and protein contents and are rich in minerals. The high fat content and enzyme (lipase, lipoxygenase, peroxidase) activities of oat cause short shelf life.

In this thesis, hydrothermal heat (125℃, 4 minutes) was used to oat flour and oat bran; and they were stored at room temperature (24±1℃) and under refrigerator (4-6℃) conditions with or without vacuum (18 weeks) using packaging material (70% polyamide and 30% polyethylene) with air, oxygen and water vapor barrier, Changes in some quality criteria (peroxide number, free acidity value, water activity and color) were monitored periodically in the samples. Dehulled and untreated oat (raw oat) was stored under the same conditions, and the change in quality criteria has been monitored for 6 weeks.

During storage peroxide value of oat flour with no vacuum stored at room or at refrigerator temperature changed between 10,5-30,3 (meq oxygen/kg) and 8-14,3 (meq oxygen/kg), respectively. It has been observed that the peroxide value of the samples applied vacuum varied between 9,6-11,9 (meq oxgen/kg) at room temperature, while it varied between 8,1-22,5 (meq oxygen/kg) at refrigerator temperature. The peroxide value of oat bran samples with no vacuum was in the range of 9,4-27 (meq oxygen/kg) at room temperature and 6,1-20 (meq oxygen/kg) at refrigerator temperature. The peroxide value of oat bran samples with vacuum varied between 4,0-15,1 (meq oxygen/kg) at room temperature and 15,0-21,2 (meq oxygen/kg) at refrigerator temperature. Free acidity values varied between 0,04-0,06% and 0,04-0,055% oat flour and oat bran, respectively. Free acidity value of the unteated oat varied between 0,06-0,264%. In oat flour samples, L*, a* and b* values varied between 83.60-88.51, −0.59-1.02, and 10.05-11.33, respectively. On the other hand, in oat bran samples, L*, a* and b* values varied between 79.30-85.94, 0.23-1.61 and 10.23-15.21, respectively. The water activity values of oat flour (0.413-0.511) and oat bran (0.454-0.534) samples increased during storage.

It has been seen that while a significant difference was determined in the peroxide value, water activity, a* and b* values (p<0,05), there was no significant difference in the free acidity and L* values of oat flour. In oat bran, similar to oat flour, while a significant difference was seen in peroxide value and water activity values (p<0,05), no significant difference was observed in free acidity and color (L*, a* and b*) values.

In the raw oat samples, while a significant difference was detected in peroxide value, free acidity and water activity, L* and a* values, there was no significant difference in b* value. While the free acidity values in oat flour and oat bran were within the limits (max <0.07%) determined by Oat Flour Standart (TS 13625) during 18 weeks, it increased to 0.26% in raw oats at the 6th week.

The peroxide value of raw oat is >15 (meq oxygen/kg) indicates that the product was stored under unsuitable conditions before processing. Accordingly, raw oat can be not be stored for a long time without heat treatment.

In general, peroxide value firstly increased and then decreased due to the formation of peroxides produced during the storage of oat flour and bran to secondary oxidation products; in oat flour with no vacuum stored at room temperature at 14th weeks; in all samples of oat bran at the 6th week, peroxide value approached the maximum 15 (meq oxygen/kg) specified for cold-pressed and virgin oils in the Turkish Food Codex “Communiqué on Oils Named by Plant” (Communiqué No: 2012/29). It was observed that the peroxide value of oat flour samples (with vacuum or no vacuum) stored at refrigerator temperature was lower than the samples stored at room temperature.

In general, it was observed that the peroxide value were lower in oat flour and oat bran stored without vacuum at refrigerator temperature. The results show that vacuum packaging and refrigerated storage partially extend shelf life by slowing oxidation in oat flour and oat bran. It has been observed that oat flour can be safely stored up to the 14th week and oat bran up to the 6th week.