Wpływ warunków przechowywania na morfologię i wielkość cząstek proszku miodowego

Proszek miodowy otrzymany poprzez suszenie metodą rozpyłową z dodatkiem maltodekstryny przechowywano przez 9 tygodni w różnych warunkach (temperatura/ /wilgotność względna: 4°C/40–45%, 25°C/40–50%, 38°C/80%). Bezpośrednio po suszeniu oraz po 1, 5 i 9 tygodniach przechowywania analizowano morfologię (mikroskop skaningowy) i wielkość cząstek (analiza obrazu) oraz oznaczano zawartość i aktywność wody. Stwierdzono, że najkorzystniejsze warunki przechowywania, które pozwoliły na zachowanie formy sypkiego proszku o nieznacznie zmienionej morfologii cząstek oraz stałej zawartości i aktywności wody przez cały okres przechowywania to 4°C/40–45%. Proszek przechowywany w temperaturze 25°C charakteryzował się stabilnymi wartościami zawartości i aktywności wody, jak również tylko nieznacznie zmienioną morfologią, ale tylko do 5. tygodnia przechowywania, po dłuższym przechowywaniu nastąpiły znaczne zmiany morfologii (tworzenie skupisk) oraz obserwowano zbrylanie proszku na skutek wzrostu zawartości i aktywności wody. Proszek przechowywany w temperaturze 38°C już po tygodniu całkowicie zbrylił się, tworząc twardą strukturę upłynniającą się w czasie dalszego przechowywania.

The influence of storage conditions (4°C/relative humidity RH 40–45%; 25°C/ /RH 40–50%; 38°C/RH 80%) and time (1, 5, 9 weeks) on the morphology and particle size of honey powder was investigated. Honey powder was produced in a laboratory spray drier Anhydro (Denmark), with the use of maltodextrin DE15 as a carrier. Spray drying of honey/maltodextrin aqueous solution (honey solids to maltodextrin solids ratio 50:50) was performed at inlet/outlet air temperature 180/80°C, feed rate 1 ml·s–1, atomization disk speed 39000 rpm. Powders particle morphology and size distribution were analyzed based on microphotographs (Hitachi TM 3000 electron microscope, Multiscan software) Water content and activity in powders after subsequent storage periods were also determined. Directly after drying powder was easy flowing, without caking. Particles were regular and scattered, particle size ranged from 8 to 33 μm, what was typical for spray dried materials. During storage the changes of powder morphology and particle size were observed, depending on storage conditions. Storage at 4°C did not affect powder morphology substantially. The powder stored at 25°C was characterized also by slightly changed morphology, but only until 5 weeks of storage. After this time significant changes in morphology were observed (aggregation), along with powder caking. The powder stored at 38°C was completely caked after 1 week of storage, turning into a hard structure that liquefied upon continued storage. A relationship between water content and water activity of powders and their morphology changes during storage was observed. Water content and activity of samples stored at 4°C did not change significantly during storage, which was related to the lack of caking. In powders stored at 25 and 38°C water content was statistically significantly higher after 5 weeks of storage, at the same time a noticeable caking of material was observed at water content of 7.1 ±2.4 (25°C), and its liquefaction at water content 11.4 ±3.1 (38°C). In case of powders stored at 38°C, statistically significant differences in water activity after each storage period were observed, which was associated with intensive caking after 1 week and subsequent liquefaction after subsequent stages. The most favorable conditions for honey powder storage, which allowed to keep the powder form with slightly altered particle morphology and constant water content and activity after 9 weeks of storage, was 4°C/40–45%. Analysis of morphology, water content and activity can be useful in controlling the quality of powders during storage. Difficulties in the application of image analysis in controlling powders quality during storage were noted, due to the aggregation of powder particles in larger, difficult to trace clusters. The dependence between water content and activity and powders morphology was observed – a significant increase in water content and activity was confirmed by caking and even liquefaction.