Mechanical properties and structure of unripe oranges during processing of “spoon sweets”

Sweetened fruits and vegetables, named “spoon sweets”, are produced by soaking in hot water and subsequent treatment with sugar solutions. Fresh small unripe oranges were processed with sucrose syrup (30%, 45% and 60%, w/v) at various temperatures (28 °C, 55 °C, 70 °C and 90 °C). Pretreatment soaking of fruits at temperatures higher than 90 °C is necessary for texture softening (up to 90% of initial texture). The mechanical properties of the fruits in warm water (55 °C, 70 °C, 90 °C) were also examined by submission to force-compression tests using a texture analysis device. Four texture parameters were selected for evaluation: hardness, failure stress, failure strain and Young’s modulus of elasticity. Mechanical properties, water loss and sugar solid gain of samples showed a strong dependence on the processing temperature, on the presoaking time and on the sucrose concentration. Increase of syrup concentration during prolonged osmotic processing at 90 °C of the presoaked samples showed a stabilization of skin firmness and strength.