Technical Development of Value-added Processed Products Using Frozen-stored 'porotan, a New Variety of Chestnut

The Japanese chestnut (Castanea crenata Sieb. et Zucc.) 'Porotan' has excellent peelability, but deteriorates due to cracking during heat-processing. The purpose of this study was to develop a kanroni (sweet-boiled) manufacturing method for frozen fruit resulting in minimal cracking of the fruit. Therefore, the effects of different kanroni manufacturing conditions (e.g., peeling and thawing methods, alum immersion time, heating temperature and the use of a lid placed deep inside the pot) on the rate of fruit cracking were studied. To further optimize the kanroni method, the effect of manufacturing conditions on color and physical properties was also studied. The best method with the lowest fruit cracking rate involved removal of the peel of the fruit through a boiling process, immersion in alum for 10 min or longer, and then boiling in hot water and sugar at 85 degrees C. The methods having the greatest effect on maximum stress were the peeling and thawing methods, alum immersion time, and heating temperature; while color was affected the most by peeling and thawing methods, and alum immersion time. We concluded that fruit peeling via a boiling process, immersion in alum for 10 min or longer, and then boiling in hot water and sugar at 85 degrees C is the optimal manufacturing method for kanroni using frozen 'Porotan' chestnuts.