The impact of germination time on the some selected parameters through malting process

Highlights

• Germination time presented the most substantial impact on malting.

• Increasing of the germination time reduced the starch quantity, beta-Glucan and malting efficiency.

• Increasing of the germination time increased beta-Glucanase and alpha-amylase enzymes, the diastatic power alongside of the hot water extract efficiency.

Abstract

In the present study, the impacts of germination time on the enzymes activity attributed in malting and some polysaccharides contents of the malt prepared from the Joseph barley variety have been screened using a completely random design with three levels of germination time(3, 5 and 7 days). The archived outcomes revealed that the highest quantity of starch has been observed in the malt resulted from 3 days germination, and an enhancement in the germination period from 3 to 7 days decreased the quantity of available starch. An enhancement in the germination period presented a reduction in the beta-glucan quantity in the malting seeds. The malt produced 7 days after germination had the highest enzymatic activity(253 U. kg⁻¹). The comparison of data average using Duncan test showed that the minimum and maximum value of α-Amylase enzyme activity and diastatic power were recorded in the malts produced 3 and 7 days after germination, respectively. Increasing in the germination time led to a reduction in malting efficiency, however the efficiency of the hot water extraction showed enhancement. The outcomes of the correlation between the studied parameters showed that the beta-glucan and starch quantities are negatively affected by the activities of beta-Glucanase and α-Amylase.

Introduction

Economic development of developing countries with similar climates and agricultural conditions depends on the expanding of agricultural industries as a main parameter in availability of job vacancies. A solution to attract foreign currency income for the upcoming years could be restriction of exiting of valuable foreign currency out of borders via reducing food products import. In this regard, the role of food processing industries is certainly undeniable. Barley with the scientific name of Hordeum Vulgar L., is among the agricultural and strategic products supported commercially regarding the recent agricultural policies and is considered as one of the important forage plants. Recently, researchers and international research centers pay considerable notice to this plant and its malting procedures. In the resent years, this issue has been significantly enhanced in Iran [1]. Malting is a combined biotechnological approach involving of steeping, germination and drying of the germinated seeds in controlled conditions of different temperatures and humidities [2]. The major purpose of germination is synthesizing of the hydrolytic enzymes to decompose the cells’ wall, protein and endosperm starch compounds leading to a desirable enhancement of brittleness and fragility of the barley grains [3]. Usually, within the germination leg, the relative humidity of the air passing through the grains' bed is almost 100% and the temperatures range are between 12 and 19 °C depending on the barley variety applied in malting. Ref. [4] reported that an enhancement in the germination time will lead to an increase in the amount of albumin and globulin contents; therefore, the amount of available soluble proteins gets increased in the obtained extract. Ref. [5] examined the physicochemical characteristics of the oat grains during germination and stated that during germination the activities of enzymes including α-Amylase, beta-Amylase and beta-Glucanase are increased, moreover the starch content is reduced from 60% to 20%, on the other hand the quantity of reducing and soluble sugars got increased, also the amount of protein showed an enhancement, but the amount of lysine got reduced at the end of the germination phase. Finally, the quantity of Phytic acid presented a reduction from 0.35% to 0.11%. Beta-Glucan is a water-soluble non-starch polysaccharide which is the main component of the polysaccharides detected in the endosperm cell walls of barley and has been made of a non-branched chains containing beta-d-glucopyranose with bonds of (1 → 3) and (1 → 4) [6]. Alterations in the quantity of beta-Glucan and the activity of beta-Glucanase in germination and malting process are presenting substantial impacts in malting, since both of the abovementioned parameters are associated with the efficiency and quality of the produced malt. Analysis of the endosperm cell walls and the subsequent changes in the beta-Glucan structures during the malting process is significantly associated with the beta-Glucanase activity [7]. Beta-Glucanase is often synthesized in the Aleurone and Scutellum of the germinated grains and remains hidden in the endosperm cells. Therefore, during the malting process, the beta-Glucan content decreases significantly as a result of enhancement in beta-Glucanase activity. Therefore, developed malting process depends on the less amounts of beta-glucan contents in the grain and higher quantities of beta-Glucanase enzyme in the obtained malt [7]. Beta-Glucanase produced during the malting process hydrolyses the cell walls into soluble beta-Dextrin with low molecular weight; it is almost thermolabile and rapidly inactivated during the extraction phase above 50 °C temperature. However, liquefying of beta-Glucan from the intact cell walls is continued and leads to the accumulation of soluble beta-Glucan molecules in the extract [8]. Temperature, humidity and period of the germination are the key factors on the final characteristics of the produced malts. High temperatures accelerate the germination process but decrease the activity of beta-Glucanase and protease enzymes. Moreover, a rapid increase is observed in the amount of α-Amylase enzyme which is decreased before the completion of the endosperm amendment [9]. In fact, extraction by hot water shows an enhancement in the quantity of dissolved solids in the sweet extract obtained from the malt or other materials added to the malting medium during the malting process in a small-scale, there is a direct relationship between the extraction efficiency of the cold water extract and changes in dissolved solids quantity within the germination process [10]. Ref. [11] stated that remaining of beta-Glucan increases the viscosity at the end of the extraction phase and decreases the filtration rate. It might be presented that decomposition and reduction of beta-Glucan quantity is attributed to increased beta-Glucanase activities, the beta-Glucan quantity in grain is greatly reduced after the accomplishment of 50% of malting process. The activity of all the decomposing factors of barley malt starch including alpha and beta-amylase, alpha-Glucosidase, limited dextrinase and the maltase are called diastatic power which is a substantial parameter in assessing of the activity of decomposing agents of starch in malting industry. Alpha and beta-amylase together are creating more than 99% of the total diastatic activity of the malt [1]. The aim of this study is to examine the impacts of germination period on the activity of the enzymes and important polysaccharides of the barley malt grains.