Structure influence on mechanical and acoustic properties of freeze‐dried gels obtained with the use of hydrocolloids

Abstract

The research is expected to show the phenomenon of structure formation when preparing and freeze-drying gels and explain the influence of the process parameters (time of aeration, the type of hydrocolloids) on the formation of the internal structure and physical properties of a dried product, especially mechanical and acoustic properties. This achievement will contribute to the development of the science of food and human nutrition, especially within the context of the popular research on aerated diet products. The expected result will be the ability to develop a new technology for producing food with a delicate texture, using the phenomenon of sublimation. As a result, designing changes in the structure of freeze-dried fruit gels with a delicate structure will be possible due to the choice of ingredients and aeration parameters in order to develop innovative food characterised by favorable nutritional, health and functional properties, which will be attractive for the consumers.

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“…This can also be explained by the results of the previous tests, since the denser and thinner structure of these discs confers better mechanical properties. Other authors report that freeze-dried gels become harder the larger the pore diameter [53], and as can be seen in Figure 8, this is also true in our case, since the reference disc (H batch) withstands the most force before breaking and also has the highest pore diameter.…”

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“…The internal structure of the freeze-dried broccoli gel was delicate, porous, which is certainly influenced by the air bubbles introduced into the gel mass while mixing the gel components ( Figure 7). Similar results were obtained Ciurzyńska et al [83] and Ciurzyńska et al [84], who studied the structure of freeze-dried gels based on a mixture of xanthan gum and locust bean gum of various compositions, and also showed that structure is porous, with variable sized pores due to the cracking of numerous air bubbles. Porosity is very important for the quality and the texture of dry foods, because has a significant effect on the physical, and mechanical properties of foods [90].…”

“…Such a low value indicates the microbiological safety of the freeze-dried gel, and with the activity of water below 0.2, enzymatic reactions are also inhibited [100]. The obtained value is similar to the water activity of freeze-dried gels with a mixture of xanthan gum and locust bean gum powder, where, depending on the aeration time, aw of 0.018-0.021 was obtained [84] and significantly lower than the water activity of freeze-dried agar gels with apple purée (0.148-0.151) [101]. The addition of hydrocolloid to thawed vegetables should not reduce water activity, as was demonstrated by Hoefler [102], who claimed that gums are substances that retain water, but do not reduce its activity by its high molecular weight, while the addition of a larger amount of hydrocolloid may affect the reduction of water activity of the product.…”

“…The high porosity of freeze-dried food is created as an effect of the absence of capillary forces during sublimation of the frozen water [92]. A similar value was obtained for freeze-dried gels with a combination of xanthan gum and locust bean gum [84,85], freeze-dried apple and potato [93]. In the case of freeze-dried strawberry gels, the porosity was in the range of ~88-91% [94].…”

“…Therefore, properly selecting the right hydrocolloids is invariably important in designing a product with specific characteristics. Such investigations were conducted by Ciurzyńska et al [83][84][85] for freeze-dried strawberry gels on the basic of low-methoxyl pectin, the mixture of xanthan gum and locust bean gum, as well as mixture of xanthan gum and guar gum. The authors showed that hydrocolloids created the structure of freeze-dried samples, which is what influenced the physical and organoleptic properties.…”