The effects of ultra‐high pressure (UHP) on 25 starches were characterized via microscopy and DSC. Furthermore, the swelling behaviour, digestibility, paste viscosity and gel formation was determined. With few exceptions B‐starches were shown to be more pressure resistant than A‐ and C‐type starches. The pressure range in which the gelatinization occurs is typical for the corresponding starch. Only some starches (e.g. waxy corn starch) show the extensive swelling and almost complete desintegration of the granules, which usually is observed after a heat gelatinization. Typical for a UHP‐gelatinization is, that most starches show very little swelling and maintain their granular character. These starches develope very little viscosity at normal paste concentrations and form pastes of smooth texture, resp. rigid gels at concentrations above 15%. Due to the limited swelling without any resp. very little solubilization of the amylose obviously the retrogradation occurs within the granules, which probably is a further reason for the quite different paste and gel properties of UHP‐gelatinized starches in comparison to heat gelatinized ones.

Annealing and heat/moisture‐treatment both cause a physical modification of starches without any gelatinization, or any other damage of the starch granules with respect to size, shape or birefringence only via a controlled application of heat/moisture. Since with respect to the application properties (gelatinization. viscosity etc.) almost idential modifications can be obtained with both treatments, there was no exact differentiation between the two treatments types. By application of both treatments as well as a combination of both to potato starch it could be demonstrated that both treatments cause completely different alterations of the internal granule structure. From the interpretation of the Brabender viscosity, the sorption isotherm, the DSC‐curves and the X‐ray diagrams it could be confirmed that a heat/moisture‐treatment always means a structure alteration from a B‐type in the direction of an A‐type structure, whereas within annealing processes the property alteration have to be explained by a modification of the binding forces between the crystallites and the amorphous matrix.

No abstract

loo+--High-pressure pretreated and frozen green beans, carrot dice or potato cubes were fluidized bed dried and compared to untreated, pressuretreated or water-blanched dried samples. Drying rates varied with pretreatments. Freezing resulted in highest drying rates. Pressure-treated and water-blanched samples retained highly acceptable colors. Freezing or hot-water blanching or high-pressure pretreatment, followed by freezing, gave good rehydration. High-pressure treatment resulted in incomplete rehydration but combined with freezing, water uptake was between 2.1 and 4.8 mug. Retention of cell wall structures of frozen samples during drying was presumed responsible for more efficient mass transfer. Texture measurements revealed significant effects of pretreatments. Pressuretreated samples had texture nearest that of the raw material. No major differences in color were observed.

378 starch/stiirke 47 (1995) Nr 10. S . 378-384 0 VCH Ve rlagsgeaellschat't mbH, D-69451 Weinheim, 1995 0038-9056/95/1010-0378$05.00+.25/0