Abstract Limiting the rate and extent of starch digestion is a major target for increasing the nutritional value of cereal-based foods. One mechanism that could be exploited is the ability of intact cell walls to protect intracellular starches from enzyme hydrolysis, but the extent to which this mechanism is valid for cereal endosperm cells is not well understood. This study aimed to isolate individual intact cellular structures from cereals, viz. wheat and sorghum, in order to elucidate the effect of intactness of cell walls on enzymic hydrolysis of entrapped starch. Intact cells were isolated from dry milled flour obtained using three grinding rolls coupled with a wet sieving technique using selected sieves having varying apertures. The intact cellular structure in wheat and sorghum hindered the hydrolysis of entrapped starch as observed from the lower extent of digestion (9 and 7%) compared to deliberately broken cells (19 and 17% under the same conditions). The extent of digestion was markedly increased once the intact cells were cooked (33 and 26% for wheat and sorghum cooked cells), but this was less than half the digestion extent of non-encapsulated cooked starches (77 and 62% respectively). Microscopic observations coupled with fluorescence labelling of enzyme, cell walls and starch suggest a) wheat and sorghum cell walls are effective barriers for access of amylase; and b) both an extensive protein matrix (particularly in sorghum) and non-catalytic binding of amylase on cell wall surfaces can limit the amylolysis of starch within intact cells. Furthermore, the presence of incompletely gelatinised starch inside cooked intact cells, suggests limited swelling of granules trapped inside the cells. This study shows how preservation of cellular matrices in cereal-based foods could be beneficial for increasing the amount of enzyme resistant starch in cereals with added nutritional benefits.

中文翻译：

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谷物胚乳中完整的细胞结构限制了体外淀粉的消化

摘要 限制淀粉消化的速度和程度是提高谷类食品营养价值的主要目标。可以利用的一种机制是完整细胞壁保护细胞内淀粉免受酶水解的能力，但这种机制对谷物胚乳细胞有效的程度尚不清楚。这项研究旨在从谷物中分离出个体完整的细胞结构，即。小麦和高粱，以阐明细胞壁的完整性对包裹的淀粉酶水解的影响。从使用三个研磨辊结合湿筛分技术获得的干磨面粉中分离出完整的细胞，使用具有不同孔径的选定筛子。与故意破坏的细胞（相同条件下的 19% 和 17%）相比，小麦和高粱中完整的细胞结构阻碍了截留淀粉的水解，从较低的消化程度（9% 和 7%）可以看出。一旦完整的细胞被煮熟，消化程度就会显着增加（小麦和高粱煮熟的细胞分别为 33% 和 26%），但这还不到未封装煮熟淀粉消化程度的一半（分别为 77% 和 62%）。显微镜观察加上酶、细胞壁和淀粉的荧光标记表明 a) 小麦和高粱细胞壁是淀粉酶进入的有效屏障；b) 广泛的蛋白质基质（特别是在高粱中）和淀粉酶在细胞壁表面的非催化结合都可以限制完整细胞内淀粉的淀粉分解。此外，煮熟的完整细胞内存在不完全糊化的淀粉，表明被困在细胞内的颗粒膨胀有限。这项研究表明，保留谷物食品中的细胞基质如何有利于增加谷物中抗酶淀粉的含量，并增加营养价值。