Effect Of Microencapsulation Of Green Tea Polyphenols On The Antioxidant,Antibacterial Activity And Quality Attributes Of Fresh Cheese

Fresh cheese is a very popular dairy products characterized by its soft texture,its whiteness and its slightly milky flavor.Fresh cheese lower calories content compared to aged cheese makes it an excellent element for an healthy diet.Due to the absence of ripening process,fresh cheese antioxidant properties are lower than other types of cheese and the spoilage occurs more rapidly.Therefore,it would be beneficial to increase the antioxidant properties of fresh cheese with antioxidant-rich compounds which can potentially extent its shelf-life.Supplementation of food products with natural bioactive components is gaining a lot of interest and green tea polyphenols are among the most promising bioactive compounds with regard to their high antioxidant properties.The consumption of green tea has been linked to the prevention and the reduction of a wide range of health conditions such as cancer,immune and cardiovascular diseases.Recently,there have also been human studies proving the beneficial effect of green tea catechins to treat metabolic syndrome,such as obesity,type II diabetes,and cardiovascular risk factors.The antioxidant properties of tea polyphenols have gained a growing attention as a way to enhance the nutritional properties of food formulation.However,despite their numerous heath promoting properties,diverse drawbacks subsist in their application to food formulations.It is the case for their sensitivity to adverse factors such as pH,temperature,light,enzymes,oxygen,making it difficult to maintain their bio-activity and bio-availability in food products.Supplementation of GTP also affect the quality attributes of the product by the occurrence of color transfer and alteration of the taste from the polyphenols bitterness.Therefore,it is crucial to develop and apply systems that can preserve the green tea polyphenols functionality from adverse factors(temperature,low pH,oxygen,etc)while providing products meeting consumers acceptability.Microencapsulation techniques which have been successfully used in the food industry,represents a propitious solution to overcome the challenge of incorporating and maintaining green tea polyphenols efficiency in food products.The encapsulation approach is an ideal solution to overcome the solubility incompatibilities between ingredients and to protect sensitive ingredients such as polyphenols from degradation.The fortification of food products with microcapsules of green tea polyphenols is a novel approach.In this manner,the present study aimed to develop and characterize microcapsules of green tea extracts,to study the effect of their application on fresh cheese antioxidant properties and quality attributes.Novel microcapsules of Chinese green tea extracts(GTE)were produced by spray drying and freeze drying using whey protein isolate(WPI),maltodextrin(MD),and their combination(WPI+MD)in 100%and 1:1 core ratio respectively.Microcapsules were characterized for their physicochemical properties,their morphological structure,and their antioxidant activity during simulated digestion and upon storage.The most effective microcapsules were then introduced at different concentration to produce a supplemented fresh cheese.The microcapsules effects on the cheese physicochemical properties,total phenolic content,antioxidant activity were studied.The antibacterial properties of microcapsules on the growth of spoilage inducing microorganisms upon storage were as well assessed.The present work can therefore serve as a technical resource for the application of microencapsulation of green tea extract for food application.The main results were as follows:(1)The microcapsules were successfully produced by freeze and spray drying.The results of the encapsulation yield revealed that all formulations of microencapsulant tested(WPI,MD,WPI+MD)showed a good encapsulation yield(ranging from 60 to 88%).The highest encapsulation yield(88%)was obtained for the freeze dried doubled coated formulation(WPI+MD)followed by freeze dried MD(72%)and spray dried(WPI+MD)(60%)suggesting a stronger protection by protein-carbohydrate complex.(2)The study of the microcapsules physicochemical properties showed that the moisture content values of the GTE microcapsules ranges from 3.02%to 4.48%.these values are in agreement with previous studies which suggested a moisture content between 3%and 5%for a better stability of green tea powders.The Bulk density values of spray dried powders were in the range of 0.38 g/cm~3 to 0.44 g/cm~3 and those of freeze dried powders from 0.51 g/cm~3 to 0.65 g/cm~3.Freeze dried powders were more hygroscopic than spray dried powders.(3)The results of the scanning electron microscopy showed that encapsulation was successful revealing 90%fully encapsulated extract.All freeze dried microcapsules appears irregular in shape with a flask-like structure while spray dried capsules on the other hand had much rounder structures.Particles size distribution,on the other hand,revealed that spray dried particles had a mean d(4,3)ranging from 50.393 to 66.082?m.Comparatively,freeze dried particles showed a mean d(4,3)ranging from 52.637 to 290.002?m.(4)The analysis of the total polyphenols content in microcapsules revealed that spray dried powders exhibited lower polyphenols content(47-58%)as compared to freeze dried powders(59%-64%).A similar trend was observed for the results of antioxidant activity,and double coating formulations of freeze dried(WPI+MD)microcapsules had the highest antioxidant activity(75%).These results indicated that the choice of the drying process plays a crucial role in preserving polyphenols content.(5)The Gas chromatography-mass spectrometry(GC-MS)identified the presence of six main catechins in the microcapsules((+)-Catechin,Epigallo-catechin gallate,Epigallo catechin,Tannic acid,Caffeic acid)which were also identified in the free extract and are known to be health-promoting catechins.(6)The results of the in-vitro test revealed that minimal release was observed when microcapsules were submitted to Simulated Gatric Fluid(low pH)while 80%of the release of polyphenols took place when submitted to the Simulated Intestinal Fluid phase.These findings were also reported by previous studies.At low pH(pH=1.2-2),the non-encapsulated samples(GTE)used as control showed severe degradation of their total polyphenolics content.For both drying methods,the rate of retention of polyphenols in the different microcapsules formulation was in order(WPI+MD)>(MD)>(WPI).The microspheres(WPI+MD)showed the highest retention capacity followed by MD while WPI exhibited the lowest polyphenols retention.It was found that the presence of MD might have possibly favored the uptake of polyphenols retention.(7)The effects of storage at 4?and 25?on the total polyphenols content of free,spray dried and freeze dried green tea extract were reported.It was found that when stored at 4?total polyphenols content in decreased in the range of 1.50-9.55 mg of gallic acid equivalents per gram.Free green tea extract exhibited the lowest retention rate in total phenols content(45%).Comparatively,it was observed that extracts prepared with either MD,WPI or(WPI+MD)were able to retain over 80%of their total polyphenols content.When stored at 25?for the same amount of time,non-encapsulated extract exhibited the lowest value of total polyphenols content resulting in the highest degradation rate 92%.Irrespective of the drying process,the retention rate in total phenols content of all formulations(WPI,MD,WPI+MD)were 68.01%,80.22%and 85.75%respectively.(8)The effect of supplementation of GTE microcapsules on the microbial growth of spoilage-inducing microorganism in fresh cheese over 30 days of storage at 4?was investigated.It was found that the supplementation of GTE did not have a significant inhibition power on Lactic acid bacteria(LAB),as their total counts increased in encapsulated GTE cheeses throughout the storage period(4.22-8.12 log CFU/g).The growth of Enterobacteriaceae,Molds,and Yeasts were significantly reduced in cheese treated with GTE compared to plain cheese and the microcapsules inhibition power in cheese samples was proportional to the concentration in GTE.In general,the antibacterial activity of GTE related to its ability to irreversibly damage the bacterial cytoplasmic membrane and their possible prebiotic action with LAB inhibiting other spoilage bacteria could possibly cause the observed delayed microorganism growth.Addition of GTE significantly delayed the growth of pathogenic microorganisms in fresh cheese which presented a shelf life of 20 days,whereas plain cheese quickly reached a total counts>6 log CFU/g in approximately 10 days.The present microcapsules can therefore be applied to extend the life of fresh cheese.(9)The changes in the physicochemical characteristics of plain cheese and cheese supplemented with free and encapsulated green tea extract over 30 days of storage were studied.There was no significant difference(p>0.05),between the values of moisture content,dry matter,fat and total protein content of the control and GTP microcapsules cheese,suggesting that the addition of GTP microcapsules did not affect the chemical composition of the cheese when it comes to the above mentioned parameters.(10)The analysis of color and texture over 30 days of storage on the cheese samples supplemented with free or encapsulated extract revealed that the use of coating material considerably(p<0.05)reduced the green color appearance in the bio-fresh cheese as compared to control.The color of the cheese sample was significantly affected by addition of GTP.The lightness L*values of the encapsulated-GTP cheese were lower compared to those of the plain cheese at concentration 2.5 and 5%,nevertheless higher than those of the non-encapsulated GTP cheese.These L*values significantly decreased with an increase of the concentration in GTP.The different parameters assessed for the texture analysis were the hardness,cohesiveness,and springiness of cheese samples.The hardness were significantly higher(p<0.05)in cheese supplemented with GTP(10.66-19.27)compared to plain cheese(5.20-5.53)throughout the storage period.It was found that addition of GTP microcapsules influences cohesiveness and springiness in cheese as the values for cohesiveness,and springiness in cheese supplemented with encapsulated GTP were slightly lower than those of the control(plain cheese).(11)The results of the sensory evaluation showed that the mean score for appearance,color,taste,and overall acceptability of the encapsulated cheese samples were liked very much(between7-9 in hedonic scale).No significant differences were observed between cheese supplemented with freeze dried or spray dried GTP microcapsules.Parameters such as texture and flavor were moderately liked(between 5-6 hedonic scale).It was observed that an increase in GTP concentration led to a decrease of the likeness scores regarding texture and flavor.The best scores were obtained for samples containing 1.5%and 2.5%concentration of GTP.The green tea polyphenols astringency as well as the incorporation of coating material could be responsible for the slightly low acceptance with regard to texture and flavor.