Starches - from granules to novel applications: Dissertation

In this study, the effects of growth temperature, starch composition and granule size on the gelatinisation and solubility properties of barley starch were studied. The mechanical properties and structures of amylose and amylopectin film, with and without added glycerol, were investigated. A novel starch-based microencapsulation method was developed for probiotic bacteria by combining native starch granules with amylose coating. The suboptimal growth conditions influenced the properties of two-rowed malting barley cultivars "Kustaa" and "Kymppi" as well as Kustaa¢s large A-granules and small B-granules. The gelatinisation temperature was lower and the rate of retrogradation less in starch grown in cold and rainy conditions. Swelling and solubility were greater and the starch was more susceptible to amylases. The small B-granules had a higher lipid:amylose ratio than the large A-granules. The B-granules also had a higher dissociation enthalpy of the amylose-lipid complex than the A-granules. Furthermore, the gelatinisation temperature was 4°C higher for B-granules than for A-granules. During heating in excess water up to 90°C amylopectin was mainly leached from the B-granules, whereas amylose was solubilised from the A-granules. At 95°C, B-granules were completely solubilised but A-granules remained partially particulate. Amylose produced good quality films from water solutions in the presence of glycerol. Film formation was successful even at a 70% glycerol content, whereas films could not be prepared from amylopectin above a 30% glycerol content. Based on calorimetric glass transition (Tg) analysis, pure glycerol was observed to decrease the Tg. However, water had a stronger plasticisation effect. No difference between the Tgs of two starch polymers could be observed. The Tg was at room temperature at a water level of 21%. Phase separation to starch-rich and starch-poor regions occurred in glycerol plasticised systems. Fresh amylose films with 0-30% glycerol at an RH of 0-91% had B-type crystallinity at a level of 6-32%, depending on the amount of water and glycerol. No changes were observed in the crystallinity of the amylose films during 2 months of storage. The fresh amylopectin films were amorphous. After a storage period of 2 months at RH 91%, the amylopectin film with 30% glycerol showed a crystalline structure but all other amylopectin films remained amorphous after ageing. Crystallisation occurred in the rubbery phase of the system. Amylose film was not fragmented or dissolved in water, and part of its structure was resistant to amylases and acid. Freeze-drying of native potato starch made the granules accessible to a-amylase, and enzymatic hydrolysis appeared to occur from the inside out, producing porous granules. The porous material was used as a bacteria carrier in a fermentation process. Dissolved high amylose maize starch solution was added after the growth period. Finally, the product was freeze-dried to produce powder.