Microscopic examination of banana, potato, wheat and oat : influence of pre-digestive processing on cellularity and structure

Abstract

Cellularity has recently become a term that describes the cellular intactness of foods. Cellular structure has been studied in the context of texture and other sensorial aspects, as well as mentioned in studies focusing on human metabolic health. As of today, no studies have mapped the cellularity of different foods and the changes in cellularity after processing and chewing, though some information exists through indirect studies. This thesis aimed to investigate differences in cellular structure and cell wall intactness in food after different processing methods, including chewing. The selected foods were potato (raw, boiled, boiled and masticated, homemade mashed and instant mashed potatoes), banana (fresh, masticated, and blended as in smoothie for 15 and 30 seconds), oat (whole, fast cooking and premium oat flakes), and wheat (whole, refined and fine whole wheat flour, commercial and stone ground milling techniques). The results were presented as micrographs and quantification of intact cells, as well as explanation of observations. Unprocessed foods, as well as boiled potato were considered to have ~100% intact cellular structure. In vivo mastication decreased the percentage of intact cells with approximately 20 in both banana and boiled potato. The results of potato and banana samples indicated a relationship between increased processing degree and decreased percentage of intact cells. For instance, lowest percentage of intact cells were found in the instant mashed potatoes and in the banana sample blended for the highest time. For cereals, both milling and rolling resulted in extensive structural destruction. In oat flakes, the particle size seemed to influence the size of the coherent aleurone layer. These studies demonstrated that some types of processing, such as grinding for smoothie production, destroyed cellular structure in banana, while other processing methods, such as boiling of whole potato did not.