بررسی تاثیر فرایند هیدروترمال بر خواص رئولوژیکی بتاگلوکان یولاف

بتاگلوکان یک پلی‌ساکارید خطی، بدون انشعاب، غیرنشاسته‌ای و محلول در آب است که در دیواره سلولی غلات به‌ویژه یولاف وجود دارد. با توجه به تاثیر فعالیت آنزیمی بر پایداری لیپیدهای یولاف لازم است که این آنزیم‌ها در طی فرآوری یولاف غیر‏فعال شوند. یکی از روش‌های موجود برای غیرفعال کردن آنزیم‌ها، فرآیند هیدروترمال است. در این پژوهش فرایند هیدروترمال با اتوکلاو در دماهای110 ، 120 و 130 درجه سانتی‌گراد در دو زمان 10 و 20 دقیقه بر روی آرد یولاف انجام شد و بتاگلوکان استخراجی از آن به روش آبی از نظر خواص فیزیکو شیمیایی و عملکردی و نیز رئولوژیکی مورد برررسی قرار گرفت. بتاگلوکان حاصل از آرد یولاف هیدروترمال شده در 120 درجه سانتی‌گراد به مدت 10 دقیقه بالاترین حلالیت را در 25 درجه سانتی‌گراد و کمترین حلالیت را در دمای 50 درجه سانتی‌گراد و تیمار 120 درجه سانتی‌گراد به مدت 20 دقیقه بیشترین حلالیت را در 75 درجه سانتی‌گراد داشت. میزان کف‌کنندگی بتاگلوکان استخراجی از آرد یولاف هیدروترمال شده در دمای 130درجه سانتی‌گراد به مدت 10 دقیقه، از سایر تیمارها کمتر بود و بتاگلوکان حاصل از تیمار هیدروترمال شده در دمای 110 درجه سانتی‌گراد به مدت 10 دقیقه از ثبات کف بالاتری برخوردار بود. در بررسی خصوصیات رئولوژیکی، تاثیر سرعت برشی بر میزان ویسکوزیته نشان داد که با افزایش سرعت برشی، میزان ویسکوزیته در تمامی نمونه‌ها کاهش یافت و بیشترین مقدار ویسکوزیته را بتاگلوکان حاصل از آرد یولاف هیدروترمال شده در دمای 120 درجه سانتی‌گراد به مدت 10 دقیقه داشت. در آزمون نوسانی شامل روبش دما، پارامترهای اندازه‌گیری شده شامل مدول الاستیک g′ و مدول ویسکوز g″ بودند که مقدار g′ و g″ در نمونه بتاگلوکان استخراجی از آرد یولاف هیدروترمال شده در تمامی نمونه‌ها کاهش یافت و نیز مدول الاستیک و ویسکوز بتاگلوکان استخراج شده از آرد هیدروترمال شده در دمای 120 درجه به مدت 10 دقیقه از سایر تیمارها بیشتر بود. در روبش فرکانس در فرکانس‌های پایین‌تر، g″ از g′ بزرگتر است و هر دو با افزایش فرکانس افزایش می‌یابند و مقدار g′ وg″ و η* بتاگلوکان استخراج شده از آرد هیدروترمال شده در دمای 120 درجه به مدت 10 دقیقه از سایر تیمارها در فرکانس 1 و 10 هرتز بیشتر بود.

The effect of hydrothermal processing on rheological properties of oat β-glucan

Introduction: Oat establishes a healthy basis for food products. It has gained relevance in human nutrition because it is one of the few cereals with a high content of soluble fiber namely β glucan, and is a good source of proteins, vitamins, and minerals (Butt et al., 2008). βglucan is one such polysaccharide that has received much attention from the past few years due to its several health beneficial properties, including the ability to remove free radicals in a way identical to antioxidants (Gardiner, 2000). βglucan is an unbranched polysaccharide consisting of βDglucopyranose units linked through (1→4) and (1→3) glycosidic bonds in cereals and (1→6) glycosidic bonds in fungal sources (Ahmad et al., 2016). βglucan from different sources vary in their molecular structure, chain conformation, solubility, number of β (1→3) or β(1→6)linkage, and thus different biological activities (Descroix et al., 2006). βglucan is regarded as an important functional ingredient to lower serum cholesterol, promote weight management, reduce glycemic response, enhance immune system, besides having a prebiotic effect (Zhu et al., 2016; Shah et al., 2016). β–glucan from barley and oat at a 3 g/day dosage as recommended by FDA would reduce cardiovascular disease risk including a reduction in blood glucose and also has satiety effects. Therefore, in order to meet the demands of people related to diets that have a low glycemic index and antioxidant property, nonstarch polysaccharides like βglucan can be used as an ingredient in the products to develop new functional foods (Lee et al., 2016). Oat grain’s fat content is more than that of wheat and it is full of lipase, lipoxygenase, and other hydrolytic enzymes. Over time, enzymes lead to the hydrolysis of the fats present in the oat that make the rancidity taste. Due to the effect of enzyme activity on the stability of oat flakes, these enzymes need to be deactivated during oat processing. One of the methods for disabling enzymes is a hydrothermal process (Doehlert et al., 2010). In this study, the effect of the hydrothermal process using autoclave on the physical and rheological properties of oat βglucans at different times and temperatures has been investigated.; ;Materials and methods: In this study, betaglucan was extracted from oats using the hot water extraction method. Hulled oat grains, it put into the autoclave for hydrothermal processing, at three different temperatures of 110, 120 and 130°Ϲ in two different times (10 and 20 minutes) intervals, to measure the effect of time and temperature on physicochemical and functional and rheological properties of βglucan. After extraction, the physiochemical and functional properties of extracted βglucan such as solubility, foaming, foaming stability and rheological properties were tested. In order to measure the moisture, ash and protein content, the standard methods (AOAC, 2005) were used. The fat content of the flour was measured by the standard AACC method 2530. The starch was determined by polarimetry method. For solubility measurement, according to BetancurAnoka (2003) method, after preparing 90 ml of 1% w / v solution from each sample βglucan, it was divided into 3 equal parts. Then each of them was placed in a warm bath of 25, 50 and 75 °C for 30 minutes. After centrifuging for 15 minutes at about 8000 g, 10 ml of the upper clear solution was transferred to an oven at 125 °C to reach a constant weight. Finally, solubility percentage at different temperatures was calculated.;The foaming capacity and foam stability were studied using the temelli method (1997). For this purpose, 2.5 g, βglucans was dissolved in 100 mL distilled water. The resulting solution was mixed vigorously for 2 min using a hand held food mixer at high speed in a stainless steel bowl with straight sides and volumes were recorded before and after whipping. To determine foaming capacity, foams were slowly transferred to a 1000 mL graduated cylinder and the volume of foam that remained after staying at 25 ± 2°C for 2 h was expressed as a percentage of the initial foam volume (Temelli et al. 1997; Ashraf Khan et al., 2016). β Glucan gum solutions were prepared in duplicate in the desired concentration (1.0% of gum, w/w) using distilled water. The rheological properties of the samples were studied by an Anton Paar Physica Rheometer (Physica, MCR 301, Anton Paar GmbH, Germany), with a parallel plate geometry.; ;Results and discussion: βglucan obtained from hydrothermal process on oat flour at 120°C for 10 minutes had the highest solubility at 25°C and the lowest solubility at 50°C, and 130°C treatment for 10 minutes had the highest solubility at 75°C from hydrothermal process on oat flour at 120°C for 10 minutes had the highest solubility at 25°C, and the treatment of 110°C for 10 minutes and also the treatment of 120°C for 20 minutes had the highest solubility at 50°C and 75°C. The amount of foam in treatment at 130°C for 10 minutes were lower than other treatments and the treatment at 110°C for 10 minutes had the highest foaming stability. In the study of rheological properties, the effect of shear rate on viscosity showed by increasing the shear rate, viscosity decreased in all samples. βglucan from hydrothermal process on oat flour at 120°C for 10 minutes, had the highest amount of viscosity. In the temperature sweep the parameters included G′ modulus and G″ modulus, the amount of G′ and G″ in β glucan sample that extracted from hydrothermal process on oat flour were decreased in all samples. Also, G′ and G″ of extracted βGlucan from hydrothermal process on oat flour at 120°C for 10 minutes was higher than other treatments. In the frequency sweep, at a lower frequency, the amount of G″ was more than G′, and both of them were increased by an increasing frequency and the amount of G′, G″ and η* at 120°C for 10 minutes was higher than other treatments in the frequency of 1 and 10 (Hz). The results showed that the hydrothermal process had a significant effect on the properties and functional properties of β glucan. Extracted β glucan sample at 120°C for 10 minutes had the highest solubility at 25°C, and the sample had the lowest solubility at 50°C. The sample treated at 120°C for 20 minutes had the highest solubility at 75°C. The foaming capacity of the sample at 130°C for 10 minutes was lower than other treatments and the treatment at 110°C for 10 minutes had the highest foaming stability. In the study of rheological properties, the effect of shear rate on viscosity decreased in all samples and the treatment of 120°C for 10 minutes had the highest amount of viscosity. In temperature sweep measurement, the amount of G′ and G″ were decreased in all samples and at 120°C for 10 minutes it had the highest amount of G′ and G″. In the frequency sweep, at a lower frequency, the amount of G″ was more than G′, and both of them were increased by an increasing frequency and the amount of G′, G″ and η* at 120°C for 10 minutes was higher than other treatments in the frequency of 1 and 10 (Hz).