Kinetyka rehydracji suszy owoców mini kiwi (Actinidia arguta)

Aktinidia ostrolistna to roślina, której jagody, znane jako mini kiwi czy kiwiberry, oprócz walorów smakowych posiadają istotne właściwości prozdrowotne. Owoce te mogą być przechowywane w warunkach chłodniczych jedynie przez kilka tygodni, dlatego wymagają szybkiej obróbki przedłużającej ich trwałość. Celem niniejszej pracy była ocena wpływu różnych metod suszenia na właściwości rehydracyjne suszy. W badaniach wykorzystano owoce polskiej odmiany ‘Bingo’ pochodzące z komercyjnej uprawy znajdującej się w okolicach Grójca. Susze otrzymano, stosując najpopularniejsze stosowanych techniki i parametry procesu, typowe dla surowców roślinnych, rehydrację prowadzono zaś w wodzie destylowanej o temperaturze pokojowej. Wykazano istotny wpływ zastosowanej techniki suszenia na właściwości rekonstytucyjne suszy. Do uzyskania produktów końcowych wymagających szybkiej rehydracji optymalne okazały się metody próżniowa i sublimacyjna, w pozostałych przypadkach możliwe jest stosowanie suszenia konwekcyjnego, mikrofalowo-konwekcyjnego oraz romiennikowo-konwekcyjnego.

Kiwiberry (Actinidia arguta) also known as mini kiwi is a popular plant which originates from Asia. Mini kiwi fruits are small, gelatinous berries with sweet-sour taste and because their skin is smooth they can be eaten entirely. Relatively high resistance of mini kiwi fruits to low temperature makes this plant very interesting for cultivation in different regions. However, short fruit storability (up to six weeks under refrigeration conditions) limits the utilization of fresh fruits and encourages seeking of effective food preservation treatments, which could retain their nutrients and utilize lower quality fruits. The aim of the study was to demonstrate influence of popular drying methods on rehydration properties of the dried fruits. Kiwiberry were prepared using most popular methods and parameters convective drying (CD), infrared-convective drying (IR-CD), microwave-convective drying (MV-CD), freeze drying (FD) and vacuum drying (VD). Rehydration was performed using distilled water at room temperature and samples were obtained after 30 min, 1, 2 and 4 hours of rehydration. The course of rehydration was evaluated on the basis of mass gain, water content change and loss of soluble solids. Dry matter content of all investigated samples varied from 86,50 to 98,93% in the case of IR-CD and VD method, respectively. Moreover, the water activity of dried fruits remain lower than 0,6 which indicated that samples were microbiologically stable. During first hour of the process the fastest (in the terms of rehydration course) method was VD, and the slowest were convective based methods. After two hours of reconstitution samples produced by FD and VD method were characterized by the fastest changes of all analysed rehydration indicators. For instance, the soluble solids loss of VD fruits after 2 hours of rehydration was equal to 0,73 whereas in the case of CD samples it was equal to 0,95. Observed differences in the kinetics were maintained till the end of the study. Moreover results obtained for samples dried by CD, MV-CD and IR-CD methods were comparable during all the process. Statistical analysis of demonstrated that both drying technique and immersion time played important role in shaping the variability of all examined rehydration determinants. However, based on partial η² values it can be stated that drying method had in some cases bigger impact on rehydration kinetics. Obtained results show that the most promising method for quick kiwiberry rehydration is VD whereas for slower rehydration CD, MV-CD and IR-CD methods should be applied.