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    Activity and bioaccessibility of antioxidants in yoghurt enriched with black mulberry as affected by fermentation and stage of fruit addition
    (Elsevier Sci Ltd, 2021) Durmus, Nihal; Capanoglu, Esra; Kilic-Akyilmaz, Meral
    Pasteurised whole milk was acidified with bacterial culture or glucono-delta-lactone (GDL) to determine effects of fermentation and pH reduction on activity and in vitro bioaccessibility of antioxidants and physical properties of yoghurt with black mulberry. Both pH reduction and fermentation were found to influence activity and bioaccessibility of antioxidants in mulberry yoghurt. Total phenolic content of the sample prepared with bacterial culture was higher than that of the sample with GDL, while there was a similar level of reduction in both samples after three weeks of storage at 4 degrees C. Fermentation with the bacterial culture yielded lower copper reducing activity but higher DPPH scavenging activity compared with acidification with GDL. Bioaccessibility of the antioxidants in in vitro gastrointestinal system was less than 25% in all samples. Addition of fruit after acidification or fermentation of milk, rather than before, resulted in higher antioxidant activity, higher consistency coefficient and less serum separation. (C) 2021 Elsevier Ltd. All rights reserved.
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    Bioactivity of Encapsulated Lemon Peel Phenolics as Affected by Maltodextrin and Foam Mat Drying
    (Wiley, 2025) Durmus, Nihal; Kilic-Akyilmaz, Meral
    Lemon peel constitutes a cheap potential resource for bioactive phenolics with antioxidant, antihypertensive, and antidiabetic activities. However, phenolic compounds are sensitive to environmental conditions and lose their activity during processing and storage without protection. In this study, a phenolic extract obtained from lemon peel was encapsulated to protect its bioactivity. For this purpose, two maltodextrins with 6- and 19-dextrose equivalent (6DE, 19DE) and whey protein concentrate were used along with foam mat drying (FMD) and foam mat freeze-drying (FMFD). The effects of maltodextrins and drying method were evaluated by determination of encapsulation efficiency, physicochemical properties, in vitro antihypertensive, and antidiabetic activities of the encapsulated extracts. In addition, encapsulated extracts were stored under adverse conditions to determine storage stability. All the encapsulated extracts were found to be in a glassy state. Maltodextrin with 6DE was the best wall material protecting the phenolic content. FMD with maltodextrin 6DE provided the highest encapsulation efficiency (97.6%) and hesperidin content (45 mg/100 g dm). On the other hand, FMFD with maltodextrin 6DE resulted in the highest glass transition temperature (97.1 degrees C), total phenolic content (6.63 mg GAE/g), and antioxidant activity (17.6 mg TE/g). ACE inhibitory activities of the encapsulated extracts were above 75% but reduced to less than 50% after storage regardless of maltodextrin DE and the drying method. FMFD with maltodextrin 19DE yielded 71% alpha-amylase inhibitory activity, which was higher than those of the other samples. alpha-amylase inhibition increased up to 83% after storage with no significant effect of maltodextrin DE and drying method. Results showed that the wall materials used in encapsulation also have an influence on the bioactivities besides the lemon peel extract. Both FMD and FMFD along with maltodextrin 6DE can be used for encapsulation. However, FMD can be preferred as a practical method with low equipment and energy costs and short processing time.
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    Bioactivity of non-extractable phenolics from lemon peel obtained by enzyme and ultrasound assisted extractions
    (Elsevier, 2023) Durmus, Nihal; Kilic-Akyilmaz, Meral
    Lemon peel waste constitutes a natural resource for bioactive phenolics with antioxidant, antihypertensive and antidiabetic activities. Bioactivities of non-extractable phenolics from lemon peel obtained by conventional heat-, enzyme-, ultrasound-, and ultrasound-enzyme-assisted extractions were evaluated in comparison with those of extractable phenolics. The antioxidant, angiotensin-I-converting enzyme (ACE), and alpha-amylase inhibitory ac-tivities and phenolic profile of the phenolic fractions were analysed. While the extractable fraction had higher total phenolic content, ascorbic acid content, and antioxidant activity, phenolic profile analysis indicated that the non-extractable fraction contained higher concentrations of phenolics especially hesperidin and hesperetin. The concentrations of hesperidin and hesperetin in the non-extractable fraction were 270.9 mg/100 g dry weight and 415.9 mg/100 g dry weight, respectively, which were about two-fold higher than those present in the extractable fraction. Moreover, ACE and alpha-amylase inhibitory activities of non-extractable fraction were stronger than those of the extractable fraction. Total phenolic content, total flavonoid content, and antioxidant activity were increased by enzyme and ultrasound treatments compared to those by conventional heat treatment. However, ACE inhibitory activities of all non-extractable fractions were similar while alpha-amylase inhibitory activity was higher in ultrasound-and ultrasound-enzyme-treated fractions. While ultrasound-assisted extraction slightly improved the yield of non-extractable phenolics, enzyme-assisted extraction yielded two-to four-fold increases in the amounts of phenolic compounds compared to heat-assisted extraction. Non-extractable phenolic fraction from lemon peel was found to have a significant potential as an antihypertensive and antidiabetic agent.
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    Recovery, Bioactivity, and Utilization of Bioactive Phenolic Compounds in Citrus Peel
    (Wiley, 2024) Durmus, Nihal; Gulsunoglu-Konuskan, Zehra; Kilic-Akyilmaz, Meral
    Citrus peels are rich in bioactive phenolic compounds with various health effects including antioxidant, antiobesity, antiinflammatory, antihypertensive, antihypercholesterolemic, antimicrobial, antidiabetic, and anticarcinogenic activities. Both extractable and nonextractable phenolics are present in significant amounts in Citrus peel with diverse bioactivities. While extractable phenolics can be recovered from the fruit peels by conventional extraction methods, nonextractable phenolics remaining in the residues must be released from the cell matrix first by hydrolysis with acid, alkali, or enzymes. Novel processing technologies can help in improvement of extraction efficiency. Extreme process or medium conditions degrade phenolics and their bioactivity where encapsulation can be applied to improve their stability, solubility, and bioactivity. Citrus peel powder including ascorbic acid and dietary fiber besides phenolics or extracts therefrom can be used as functional food ingredients to extend shelf life and provide health benefits. In addition, phenolic extracts can be used as antioxidant and antimicrobial agents in active food packaging applications. Phenolic extracts have also a potential to be used as nutraceuticals and pharmaceuticals. In this review, phenolic compounds in different forms in Citrus peels, their recovery, bioactivity and possible applications for upcycling in the industry are presented.