Influence of hydrocolloids in low-moisture foods – a food polymer science approach

Abstract

The “food polymer science” (FPS) approach was developed to study glasses and glass transitions, and their effects on processing, product quality and storage stability, in foods. Since 1980, this “new” approach to food research – beyond that of the “water activity” concept of moisture management – has been fruitfully used to understand structure-function relationships, the effects of plasticization by water – as illustrated by means of state diagrams – on thermal, mechanical, rheological and textural properties, and physical (meta)stability in the non-equilibrium glassy solid state, vs. instability in the rubbery or viscous liquid state. Key concepts of the EPS approach, especially as it has been widely applied in the decade of the 90's to low-moisture, hydrocolloid-containing food systems, include a practical understanding of the significance of the glass transition temperature, Tg, and its temperature range, how Tg is defined for multi-component, aqueous amorphous blends, and how Tg relates to the relative mobilities of individual components, including water, in such blends. Due to water's well-known plasticizing effect on many different food polymer systems, Tg decreases monotonically with increasing moisture content, but the linear relationship is between Tg and system relative humidity (% RH), rather than moisture content. Like the glass transition itself, plasticization is a kinetic process, so the mere presence of water is not a guarantee that softening or other changes in rheological properties have already occurred. Selected examplex of some applications of the FPS approach to studies on food processing, product properties and storage stability will be given, which illustrate the significant progress made in recent years, based on amorphous product technology. With a focus on low-moisture baked goods such as cookies and crackers, we'll first discuss the relationships among the sensory textural attribute of crispness, the glassy solid state below Tg, moisture uptake, and resulting water plasticization that leads to a loss of crispness for the rubbery liquid state above Tg. Then we'll discuss the detrimental influence of water-soluble pentosans (high MW, non-starch polysaccharides), one of the three functional components found in all wheat flous used for biscuit making, and how Nabisco's patented pentosanase enzyme technology has been commercialized to successfully overcome several different negative effects of soluble pentosans in biscuit flours.