Granule size link to starch blend properties: study

Starches have widespread uses in the food industry, but as the researchers of the new study accepted for publication in Food Researcher International​ pointed out, in its native form its functional properties are not always optimised. This means that starch is often chemically modified to improve its properties. The problem is, however, that consumers are veering away from foods that contain artificial and chemically-adapted additives - as modified starch must be labelled. This means that there is an upsurge of interest in other, non-chemical ways of improving the functionality. The researchers from Thailand said that one possibility is the blending of different starches, to improve properties such as pasting, texture, and stability. In some cases the starches act independently of each other, each bringing their own properties to the formulation (additive). In others, however, the starches were seen to interact and influence each others' behaviour (nonadditive). The research team therefore looked into both the intrinsic properties of certain blends (in particular the temperature at which gelatinisation occurs) as well as relative size of the granules. They worked with canna starch as the fixed component, which has a granule size of 52µm and a gelatinisation temperature of 72.4 ºC, and potato (48µm, 65.8ºC), mung bean (24µm, 70.1ºC) and rice starches (7µm, 75.2ºC) as the counterparts. The ratios of blends investigated - canna to each of the others - were 100:0, 75:25, 50:50, 25:75, and 0:100. They were assessed for their pasting profile, thermal property, morphology and texture, and these properties were then discussed in relation to their relative granule size and gelatinization temperature. Amongst the findings on gelatinisation (heating), the three most pertinent points were that:

• Gelatinisation of potato had little or no effect on subsequent gelatinization of canna starch;

• It was not clear whether melting the mung bean starch in advance affected its gelatinization properties;

• And there as seen to be a mutual effect ton gelatinisation between canna and rice starch.

"The results suggested that gelatinization behaviour of starch blends could be either additive or nonadditive, and relative granule size rather than gelatinization temperature of the starch components may be responsible for this behaviour,"​ wrote the researchers. The researchers then went on to look at the gelation behaviour during cooling down, and determined their hardness with a texture analyser. They found that the canna and potato starch blends had setback values that were "more or less the sum of contributions from the two starches".​ The setback values of the canna-mung bean and canna-rice starch blends, however, was not the sum of the contributions of each starch type. The hardness values appeared to mirror this trend. The canna-potato blend seemed to be additive, where as canna-mung bean and canna-rice blends seemed to be non-additive. The researchers concluded that the blending combination that affects gelatinisation would also affect retrogradation behaviour of the starch. ​"Therefore it was possible (though still unclear) that relative granule size also affected the gelation behaviour of the blends,"​ they wrote. Source ​ Food Research International (online ahead of print) DOI: 10.1016/j.foodres.2008.03.012 "Effects of relative granule size and gelatinization temperature on paste and gel properties of starch blends" ​Authors: Santhanee Puncha-arnon, Worayudh Pathipanawat, Chureerat Puttanlek, Vilai Rungsardthong, Dudsadee Uttapap