Fortified and freeze-dried kiwi fruit (Actinidia deliciosa): quality and sensory assessment

Abstract Kiwi fruit (Actinidia deliciosa) (KF) is one of the best fruits available due to its large amount of nutrients. Despite its many health benefits, there are no previous reports on its preparation in other readily ingestible forms. The objective of the present study was to make a new food product from KF. The KF pulp was fortified and blended with several raw materials (such as rice flour and oat flour) using a stepwise short time addition and mixing methodology since this avoids unwanted biochemical and chemical reactions. The blended and reduced moisture KF paste was freeze-dried on a round silver coated steel plate (RSCSP), supplying the heat of sublimation using a newly designed cubic heater. The freeze-drying (FD) time was 4.5 h and the drying kinetics were studied using four established models. The effective moisture diffusivity (Deff) during FD (at 50 °C) was 1.532 x 10-6 m2/s and the activation energy (E) estimated for the FD was 28.35 kJ/mol. The freeze-dried sample was ground and placed under vacuum to reduce the weathering effects. The quality of the stored product was evaluated using the proximate analysis, physicochemical analysis and a sensory evaluation using a hedonic scale. The raw, fresh KF had a moisture content of 85.07% and the final freeze-dried product one of 3%. The carbohydrate, total sugar, protein, fat, total ash, crude fibre and vitamin C contents of the final product increased by 563%, 400%, 355%, 386%, 672%, 106%, and 117% respectively. Of the 66 panelists, the % consumer acceptances for the different attributes were: sweetness (68.18%), sourness (90.91%), saltiness (100%), bitterness (100%), flavour (95.45%), texture (77.27%) and overall acceptability (81.82%). Using conventional freeze-drying (CFD) for blended KF pulp without fortification, with the same RSCSP and the same cubic heater for sublimation, the drying time was found to be 7 h to reach the same final moisture content of 3%.

摘要：美味猕猴桃（Actinidia deliciosa，简称KF）因富含多种营养成分，属于优质水果之列。尽管其具备诸多健康益处，但目前尚无将其制备为其他易食用形态的相关研究报道。本研究旨在以KF为原料开发一款新型食品。研究采用分步短时添加混合工艺，将KF果肉与米粉、燕麦粉等多种原料进行强化复配，该工艺可有效避免不必要的生化与化学反应。将复配降湿后的KF浆料置于圆形镀银钢板（round silver coated steel plate, RSCSP）上进行冷冻干燥（freeze-drying, FD），通过新型设计的立方加热器提供升华所需热量。本次冷冻干燥时长为4.5小时，并采用四种已成熟的动力学模型对干燥过程进行研究。在50℃条件下进行冷冻干燥时，有效水分扩散系数（effective moisture diffusivity, Deff）为1.532×10^-6 m²/s，该冷冻干燥过程的活化能（activation energy, E）估算值为28.35 kJ/mol。将冷冻干燥后的样品研磨后置于真空环境中，以降低风化对产品的影响。通过常规营养成分分析（proximate analysis）、理化分析以及采用快感评分量表（hedonic scale）进行的感官评价，对贮藏产品的品质进行评估。新鲜原生KF的水分含量为85.07%，最终冷冻干燥产品的水分含量为3%。最终产品中的碳水化合物、总糖、蛋白质、脂肪、总灰分、粗纤维以及维生素C含量分别提升了563%、400%、355%、386%、672%、106%与117%。在66名评审员中，各属性的消费者接受度百分比分别为：甜度68.18%、酸度90.91%、咸度100%、苦味100%、风味95.45%、质地77.27%以及综合接受度81.82%。采用常规冷冻干燥（conventional freeze-drying, CFD）工艺，对未强化的复配KF浆料进行干燥，使用相同的RSCSP与立方加热器提供升华热量，结果显示达到相同的最终水分含量3%所需干燥时长为7小时。