Physicochemical changes in barley starch during malting

Abstract

The objective of this work was to study the physicochemical modifications of starch during the malting of barley. The results showed that malting modifies the physicochemical properties of the starch over time by the action of barley enzymes. The gelatinisation temperature of starch increased as a function of the malting time owing to the selective enzymatic attack. The viscosity of starch decreased through malting. During germination, scanning electron microscopy showed that the enzymes degrade some starch granules which exhibited micro-holes on the surface. X-ray diffraction showed an apparent increase in the crystallinity during the first three days of germination, reflecting the consumption of amorphous regions. Such changes have not been previously reported. Infrared spectroscopy (1200-1500 cm À1 ) showed the unfolding of carbohydrates as a result of enzymatic action. Such changes in the physicochemical properties of starch indicate that the amorphous area is consumed in the early stages of malting.

Physicochemical and morphological changes in corn grains and starch during the malting for Palomero and Puma varieties

“…Some of them are fractioned, although some remain without apparent changes. The same behaviors were found during the germination of barley (Contreras‐Jiménez et al ()). Figure i and j shows the last day of germination (day 3), and micro‐ and submicron holes increase in the surface.…”

“…For the third day of germination and the malted sample, there is an apparent increase in the amylose that could be related to the amylopectin debranching. Other works observed the same phenomenon (Contreras‐Jiménez et al, ; Greenwood & Thomson, ; Swanston, Ellis, & Stark, ).…”

“…The changes in the amylose content in starches obtained along the malting process for Palomero and Puma are shown in Figure a. In this figure, the changes in this parameter reported by Contreras‐Jimenez et al () for barley are showed. The apparent amylose content decreases until the second day of germination due to the enzymatic process (Gupta, Abu‐Ghannam, & Gallaghar, ).…”

“…All tests were carried out in a constant frequency of 193 rpm (Rincón‐Londoño, Millan‐Malo, & Rodriguez‐Garcia, ; Rincón‐Londoño, Vega‐Rojas, et al, ). The values of the peak viscosity for Puma, Palomero, and malt (Contreras‐Jimenez et al, ) were compared.…”

“…The chemical composition of grains changes during the malting because the nutrients are used for the development of the pedicel and roots. The malting includes three main steps: soaking (up to 48 hr), germination (1–5 days) in which some part of starch is degraded to smaller molecules known as disaccharides, and drying stage to obtain the base malt (Contreras‐Jiménez et al, ). These changes are produced mainly by the action of enzymes such as phosphorylase, α‐glycosidase, and α‐amylose (Gupta, Abu‐Ghannam, & Gallaghar, ).…”