Impact of thermal pretreatment on crystallization of Thompson raisins

• Published in: Food chemistry Vol. 317; p. 126381
• Main Authors: Alvarez, Lorena, Urrutia, Paulina, Olivares, Araceli, Flores, Agustín, Bhandari, Bhesh, Truong, Tuyen, Almonacid, Sergio
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-07-2020
• Subjects: Chilean raisins; Crystallization; Relative humidity; Sugaring; Temperature; Relative humidity; Temperature; Chilean raisins; Sugaring; Crystallization
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2020.126381

•The increase in the ambient temperature from 15 °C to 25 °C favored the crystallization.•Thermal pretreatment of raisins at 50 °C for 12 h and 48 h reduced sugar crystallization.•During pretreatment, the crystallization was temperature- and humidity independent.
After prolonged storage or during the shipment of raisins, a crystalline material may be developed on their surface, affecting the final acceptability of the product. The mild thermal pretreatment (50 °C for a period of 12 h and 48 h) was applied to dissolve any potential tiny crystals and nuclei already present in the raisins. The thermal pretreatment of raisins resulted in a reduction on the percentage of crystallized raisins (w/w) from more than 46% in control samples to less than 10% after 30 days of storage at 57% and 66% of relative humidity and 15 °C and 25 °C. X-ray diffraction analysis identified d-Glucose monohydrate as the main crystalline component. All the thermal treatments increased the hardness of the raisins, when they were incubated at 57% relative humidity. To mitigate the problems of crystallization of raisins during shipping, it is recommended that the raisins are thermally pretreated and the shipping conditions are controlled.