Food powder

The objective of this study is to investigate the effects of the drying and grinding treatments on the physical and technological properties of flour produced from prickly pear cactus stem (Opuntia ficus-indica f. inermis). A lot of previous research has uncovered the striking nutritional and functional value of the plant's stems, which can be mainly attributed to their high content of dietary fiber. At the same time, the presence of mucilage, which is a polysaccharide with hydrocolloidal rheological properties, shows promise as a thickening agent suitable for inclusion in many types of food products.
During the experimental procedure 4 samples of cladode flour were produced by combining two different drying processes and two different grinding operations. After being cut up into uniform rectangular pieces, cladodes were predried at a temperature of 45o C in a forced air drying oven and then finally dried in a vacuum oven set up either in 45o C or 60o C. The two distinct batches of dehydraded cactus stem produced were then ground to flour in a hammer mill, and half of the produced flour were reprocessed in a jet mill. Finally, after the final preparation of the 4 samples, analysis of the particles' shape and size, their colour values, solubility, WHC and OHC, moisture and dietary fiber content, and finally, the rheological properties and sedimentation rates of 5% w/v dispersions of them in distilled water, were conducted.
Flour samples were separated as coarse and fine flours, showing significant changes in median particle size during grinding. Both processes caused intense changes in the color properties of the flours, with the higher final drying temperature resulting in a slightly heat-degraded product. Moisture and water activity were found to be low enough for the samples to be proclaimed stable and safe from microbial, enzymical and oxidative degradation (0.2 < aw < 0.4), while bulk density reduction was observed during final drying at 60°C. Suspensions of all samples exhibited pseudoplastic behavior and dependence of viscosity on temperature, while reprocessing of the flours in the jet mill was found to alter their rheological properties, possibly due to destruction of the mucilage's structure. Dietary fiber content was found to be extremely high for all samples 13 (> 40%), but no safe conclusions can be drawn for the influence of drying and grinding treatments. Solubility and oil retention capacity were mainly affected by grinding, while the water retention capacity was reduced by increasing the final drying temperature of the cladodes. Finally, all flour suspensions were judged to be extremely unstable during the sedimentation test.
Based on the results of the present study, it is evident that both heat treatment during drying and grinding of prickly pear tree significantly affect the physical and technological properties of the resulting flour, while further investigations of the milling techniques and their influence are deemed as necessary. At the same time, the extremely high dietary fiber content, combined with its interesting rheological properties, suggest a possible use for the cladode flour as a texture modifier in functional food and nutraceutical products.

Pink guava guavas are highly perishable, the implication of modern drying techniques might have enormous benefits to reduce the huge wastage during peak season. The most successful methods for fruit powder production are freeze drying, foam mat drying and spray drying (Chopda and Banrett, 2001). Stickiness is one of the major problems during drying of fruit juices or puree especially in spray drying which leads to wall-deposition problem (Patil et al., 2014)). However, maltodextrin has the ability to reduce the stickiness problem (Cabral et al., 2009). The maltodextrin added can affect powder properties. Although it is claimed that freeze drying is good in nutrient retention, but it involves with expensive operation. Hence, the comparative investigation between freeze drying and spray drying of pink guava might be more significant.

Recently, there is a growing interest in incorporating cactus cladode flour in foods, in order to improve their nutritional value, while cactus cladode mucilage exhibits potential as a thickener. In the present study, cladodes from Opuntia ficus-indica were dried at 45 oC in a hot air dryer for 24 hours, followed by a 18 hours long drying in a vacuum oven at two different temperatures (45 or 60 oC). The dried cladodes were then ground with two different methods (hammer mill or hammer mill followed by jet mill). The physical and rheological properties of the four flours were studied. Color parameters were affected both by drying and grinding process. Cladode flour aqueous solutions (5% w/v) exhibited a non-Newtonian shear thinning behavior, while micronization with jet mill led to lower apparent viscosity values for the tested shear rate range (0.3-300 s-1). These findings show that micronization of cladode flour deteriorates its thickening capacity.