Microstructure and texture of khoa and gulabjamun made from cows' milk: Heat‐induced changes during processing and frying

Abstract

AbstractScanning and transmission electron microscopy was carried out to study heat‐induced structural changes that occur during the processing of khoa (a heat‐desiccated Indian milk product) and gulabjamun (a product obtained by frying khoa, admixed with starch, in clarified butterfat and subsequently soaked in 60% sugar syrup). Constant boiling of milk during khoa manufacture led to the formation of casein‐whey protein complexes, which coalesced gradually on the progress of boiling, forming a fuzzy‐agglomerated mass and finally precipitated as heat‐induced milk gels, joined together by thick protein bridges. Further heat desiccation of this gel resulted in the compaction of the protein agglomerates with reduction in void spaces and fat globules interspersed in between (ie khoa). Frying of khoa in clarified butterfat resulted in the enlargement of the voids, producing a loose matrix having starch particles interlinked loosely with the agglomerated protein bodies and the clumped fat globules cemented in it (ie gulabjamun). The laboratory and market gulabjamun had significant structural similarities in the fat and protein moieties but differed markedly in the textural values, probably due to the differences in the chemical composition and typical structural manifestations of the starchy materials in the market gulabjamun. Composition and texture can be explained by the microstructural attributes for both khoa and gulabjamun.