Antioxidant Activity and Quality Characteristics of Yogurt Added Green Olive Powder during Storage

Enhancing Set-Type Yoghurt With Olive Leaf Extract: A Comparison of Powdered Addition and Surface Spraying on Quality, Functionality, and Sensory Attributes

In this study, the effects of using powdered olive (Olea europaea L.) leaf extract (POLE) in yoghurt at different treatments and concentrations on the physicochemical, textural, functional, microbiological, and sensorial aspects of yoghurt were investigated. Accordingly, the enrichment of yoghurts with POLE was carried out by spraying aqueous solutions of POLE (0.4% and 0.6% solution) on the yoghurt surface after fermentation and adding POLE (0.4% and 0.6% w/v) to yoghurt before fermentation. While both POLE treatments caused no difference in the total solids, fat, protein, and ash contents of yoghurt, yoghurts sprayed with olive leaf extract aqueous solution exhibited similar results to the control regarding color and textural properties. Nevertheless, yoghurt enriched with POLE before fermentation showed higher total phenolic content and antioxidant properties. POLE treatments of yoghurt provided the expected antimicrobial effect without causing any change in the viable counts of yoghurt bacteria among the samples during 28 days of storage compared to plain yoghurt. Furthermore, surface spraying of POLE aqueous solution prevented the occurrence of an undesirable bitter taste in yoghurt resulting from the addition of POLE before fermentation. These results reveal that olive leaf, which is a cost-free waste product of the olive industry, can be used as a potential antimicrobial and functional agent. In addition, the positive sensory results obtained by spraying POLE aqueous solution on the surface after fermentation suggest that this application may be an alternative method for using herbal extracts.

Encapsulation of Heracleum persicum essential oil in chitosan nanoparticles and its application in yogurt

Heracleum percicum essential oil (HEO) at various levels was encapsulated in chitosan nanoparticles and its potential application in yogurt was investigated. The values obtained for encapsulation efficiency, loading capacity, mean particle size, and zeta potential of nanoparticles were 39.12-70.22%, 9.14-14.26%, 201.23-336.17 nm, and + 20.19-46.37 mV, respectively. The nanoparticles had spherical shape with some holes as a result of drying process. In vitro release studies in acidic solution and phosphate buffer solution indicated an initial burst effect followed by slow release with higher release rate in acidic medium. Results of antibacterial activity revealed that Staphylococcus aureus and Salmonella typhimurium with inhibition zones of 21.04-38.10 and 9.39-20.56 mm were the most sensitive and resistant bacteria to HEO, respectively. Incorporation of encapsulated HEO into yogurt decreased pH and increased titratable acidity due to stimulation of starters' activity. Interaction of nanoparticles with proteins decreased syneresis in yogurt. Regarding antioxidant activity, a higher value was observed in yogurt containing encapsulated HEO after 14 days of storage due to degradation and release of essential oil from nanoparticles. In conclusion, application of HEO nanoparticles in yogurt could be a promising approach for development of functional food products such as yogurt with enhanced antioxidant properties.

Encapsulation of bioactive compounds extracted from date palm seeds (Phoenix dactylifera L.) and their use in functional food

Liposomes have been used as a novel phytoconstituent delivery system to encapsulate lyophilized palm seed phenolic extract (PSPE) and incorporate it into yogurt as a food model to enhance the bioavailability of PSPE. Phenolic compounds were extracted with aqueous ethanol from palm seed powder using the solvent-maceration approach assisted by ultrasonication. Lyophilized PSPE (0.2-1% w/v) was enclosed in a liposome structure coated with or without chitosan (primary/secondary liposome). Particle size, zeta potential, encapsulation efficiency (EE), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) were applied to investigate the primary and secondary liposomes. To assess the in vitro bioaccessibility of PSPE and primary/secondary liposomes, the total phenolic content (TPC) and the antioxidant activity were studied during the oral, gastric, and intestinal digestion stages. Three concentrations of lyophilized secondary liposomes (1.25, 2.5, and 3.75% w/v) were added to the yogurt food model. During the 14 days of storage, the physical, chemical, and sensory properties were assessed. Compared to the primary liposomes (87%), the secondary liposomes (91%) showed a higher encapsulation efficiency. Comparing the secondary liposomes to the original liposomes and the non-encapsulated PSPE, the bioaccessibility of phenolic compounds was improved. Fortified yogurt with secondary liposomes had a lower syneresis and viscosity than the reference yogurt. The encapsulated PSPE provided a good level of protection, and its release increased throughout the intestinal phase. Thus, PSPE in a microencapsulated form has been proven to be a rich and cost-effective source of phenolics that can be used successfully to produce functional yogurt.

Development and characterization of lactose-free probiotic goat milk beverage with bioactive rich jambo pulp

Goat milk is considered a suitable matrix for the successful incorporation of probiotics, also obtaining new lactose-free fermented products can expand its use. This study aimed to develop and characterize formulations of lactose-free probiotic fermented goat dairy beverages as well as to determine the most appropriate concentration of red jambo pulp to be added. The beverages were developed with different concentrations of lactose-free goat milk and frozen jambo pulp (12, 15 and 18% w/v) and lyophilized (3, 6 and 9% w/v), corresponding to formulations F1 to F6, respectively, as source of bioactive compounds. Probiotics counts decreased significantly (from 8.58 to 7.38 log CFU mL-1). The formulation with a higher proportion of lyophilized (F6) pulp showed the highest levels of phenolic compounds (72.08 mg GAE 100 g-1), anthocyanins (50.80 mg cyanidin-3-glycoside 100 g-1), ascorbic acid (41.68 mg 100 g-1), and antioxidant activity (16.21 μmol TE g-1) (P < 0.05). On the other hand, F3 presented the highest global acceptance and purchase intention (P < 0.05). However, the principal component analysis (PCA) indicated that the components related to bioactive compounds (PC1) stood out on sensory attributes (PC3 and PC4) and, therefore, F6 was most appropriate for obtaining a lactose-free goat probiotic fermented milk with improved bioactive properties targeting lactose intolerant consumers and those who are allergic to bovine milk proteins.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05399-z.

Comparative Physicochemical, Microbiological, Antioxidant, and Sensory properties of pre- and post-fermented yoghurt enriched with olive leaf and its extract

This study investigated the comparative effect of yoghurt samples enriched with different concentrations of olive leaf powder (OLP) (0.1, 0.5, 1, and 1.5 mg/ml) and its extract (OLE) (0.5, 1, 3, and 5 mg/ml) on the microbiological, sensory, physicochemical, and antioxidant properties of pre- and post-fermented samples during 21 days of storage. Sensory evaluation showed that concentrations lower than 1.5 and 5 mg/ml of OLP and OLE, respectively, were acceptable. Adding OLP or OLE did not have an influence on yoghurt starter culture bacteria (p > .05). All enriched samples significantly showed higher acidity and lower pH compared with control samples (p < .05). The most important polyphenols were oleuropein (from 0.132 to 0.224 and 0.373 to 0.413 mg/g for 0.5 and 3 mg/ml of OLE, from 0.194 to 0.321 mg/g and 0.413 to 1.280 mg/g for 0.5 and 1 mg/ml of OLP, respectively) and catechin (from 0.369 to 0.382 and 0.461 to 0.477 mg/g for 0.5 and 3 mg/ml of OLE, from 0.386 to 0.405 mg/g and 0.310 to 0.710 mg/g for 0.5 and 1 mg/ml of OLP, respectively) in enriched yoghurts. Adding OLP or OLE increased shelf life, antioxidant activity percentage (AA%), and total phenol content (TPC) of enriched samples (p < .05). During 21 days of storage of all samples, TPC, AA%, and pH decreased and TTA increased.

Effect of Encapsulated Beet Extracts (Beta vulgaris) Added to Yogurt on the Physicochemical Characteristics and Antioxidant Activity

Beet has been used as an ingredient for functional foods due to its high antioxidant activity, thanks to the betalains it contains. The effects of the addition of beet extract (liquid and lyophilized) on the physicochemical characteristics, color, antioxidant activity (AA), total betalains (TB), total polyphenols (TP), and total protein concentration (TPC) were evaluated on stirred yogurt. The treatments (T1-yogurt natural, T2-yogurt added with beet juice, T3-added extract of beet encapsulated with maltodextrin, and T4-yogurt added with extract of beet encapsulated with inulin) exhibited results with significant differences (p < 0.05). The highest TB content was observed in T2 (209.49 ± 14.91), followed by T3 (18.65 ± 1.01) and later T4 (12.96 ± 0.55). The highest AA was observed on T2 after 14 days (ABTS˙ 0.819 mM TE/100 g and DPPH˙ 0.343 mM TE/100 g), and the lowest was found on T1 at day 14 (ABTS˙ 0.526 mM TE/100 g and DPPH˙ 0.094 mM TE/100 g). A high content of TP was observed (7.13 to 9.79 mg GAE/g). The TPC varied between 11.38 to 12.56 µg/mL. The addition of beet extract significantly increased AA in yogurt, betalains being the main compounds responsible for that bioactivity.

Effects of Lotus (Nelumbo nucifera) Leaf on Quality and Antioxidant Activity of Yogurt during Refrigerated Storage

The supplementation with natural ingredients that are rich in polyphenols could improve the quality and functionality of yogurt. Lotus leaf (LL) are abundant in phenolic compounds. We aimed to investigate the effects of LL powder on the quality properties, total phenolic content (TPC), and antioxidant activity of yogurt. Yogurt was supplemented with four different concentrations (0%, 0.2%, 0.5%, and 1%) of LL powder and evaluated for 14 d refrigerated storage. During storage, the titratable acidity (TA) of all LL yogurt groups was higher than that of the control (p<0.05). The L* and a* values decreased by LL addition to the yogurts, while the b* values increased. All LL yogurt groups indicated better viscosity than that of control, and among them, 0.2% LL yogurts had the highest viscosity without significant decrease until the end of the storage duration. The addition of LL into yogurt enhanced the water-holding capacity (WHC) by at least 1.5-fold than that of control for the entire storage duration. The TPC of yogurts gradually increased with the addition of LL (p<0.05) and continued to increase during storage; the 1% LL yogurt at 14 d showed the highest value of 61.94±1.68 μg GAE/g. The DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity and reducing power of the yogurts were also significantly enhanced with increasing LL concentrations (p<0.05). These results suggest that lotus leaf may be useful as a natural ingredient for improving the quality and antioxidant activity of yogurt.

Evaluation of Physicochemical and Antioxidant Properties of Yogurt Enriched by Olive Leaf Phenolics within Nanoliposomes

Olive leaf extract is a rich source of phenolic compounds and oleuropein which is well-known regarding its antioxidant and antimicrobial attributes. However, the mentioned phenolic compounds will lose their beneficial properties during storage and induce undesirable aftertaste in food products. In this study, olive leaf extract-bearing nanoliposomes were produced via the ethanol injection method and using phosphatidyl choline plus cholesterol as the reagents for the wall material. Later, the prepared nanocarriers were examined in regard to their zeta potential, stability, encapsulation efficiency, and particle size. Moreover, the prepared nanoliposome-loaded yogurt samples were examined considering syneresis, antioxidant activity, pH, acidity, color, and sensorial properties. The mean particle size of the fabricated nanoliposomes was in the range of 25-158 nm. Also, the entire formulation had a negative charge. The encapsulation efficiency was between 70.7 to 88.2%. Besides, the application of nanoliposomes in yogurt improved the antioxidant activity, and unlike the yogurt with nonencapsulated olive extract, no significant changes in color and sensorial attributes were observed and even the syneresis rate was minimized. To conclude, olive leaf phenolics can be entrapped within nanoliposomes with a considerable encapsulation efficiency for application in food products like yogurt to increase their nutritional value and public acceptance.