| Chinese jujube,mostly grown in China is rich in nutritional and nutraceutical values,and helps in treatment of so many diseases.It is mostly preserved by drying.One of its product is jujube powder,which is amorphous in state and prone to caking when exposed to environmental conditions,which has negative impact on product manufacturability and quality.Therefore,preventive measures such as anticaking agents are added in small quantities to prevent caking and improve flowability.In addition,the quality of jujube available commercially depends on the contents of bioactive compounds such as polyphenols,flavonoids,which may change due to varying factors.Therefore the importance to study the physico-chemical changes that occur in jujube powder before and after caking.These results were obtained:Effects of freeze drying,infrared drying,instant controlled pressure drop drying,heat pump and hot air drying methods on caking of jujube powders were quantified by using the powder rheometer.In general,nonhomogeneous caking of jujube powder was observed.Drying methods showed significant effect on the caking of jujube powder.Powder dried by freeze drying and instant controlled pressure drop drying showed highest and lowest crust strength(622 and 170 mJ/g)at 25 °C,75 % RH for 5 h,respectively.Strength of caking increased with rising of RH and load.Temperature and time showed coupled effect on powder caking and higher temperature could significantly accelerate caking strength of powders.When the moisture content of jujube powder was over 0.066 g/g at 25 °C,glass transition would happen.Structure of jujube powder would change from “amorphous glassy” to “amorphous rubbery”.Caking of particles was mainly due to sinter bridge formation and fructose was one of the main contributors to caking of jujube powder.To reduce caking,anticaking agents(calcium stearate,magnesium stearate and silicon dioxide)were added at low quantity(2% w/w)to increase stability and maintain free flowing properties of the powder.Addition of anticaking agents significantly affected the moisture sorption and crust strength formed during caking of jujube powders as calcium stearate proved to be a better anticaking agent to improve flowability and delay onset of caking with lowest moisture content(0.039 g water/ g sample).Concentration of calcium stearate at 2% w/w,mixing time at 5-20 min could give a better flowability of jujube powders and delay the onset of caking.Lower and higher mixing speeds,increasing temperatures could speed up caking rate in powder blends.State diagrams established based on moisture sorption isotherm and glass transition curves showed that jujube powders with and without calcium stearate addition were stable at 25 °C when water content was lower than 0.095 and 0.088 g water/ g sample respectively.To analyze the bioactive components from jujube powder and taking into account their changes along in vitro gastrointestinal digestion,instant controlled pressure drop drying(DIC)and freeze-drying(FD)powders were subjected to caking prior to in vitro digestion.Results showed that caking significantly influenced total phenolic,flavonoid content and antioxidant activity value for jujube powders prior to digestion.However,a loss in total phenolic,flavonoid content and antioxidant activity were recorded following digestion.In general,caking had a significant influence from the mouth phase of digestion,as additional losses were observed at the stomach phase.Additionally,positive correlation between total phenolic contents and antioxidant capacities were found for powders before and after caking.Justifying that phenolic compounds are mainly responsible for the antioxidant activity.Finally,caking showed a significant influence on bioaccessibility of total phenolic components of jujube powder as it decreased from 63% to 48% after caking. |
PDF Full Text Request