Role of Ascorbic Acid in the Extraction and Quantification of Potato Polyphenol Oxidase Activity

The ability to accurately measure the activity of polyphenol oxidase (PPO) in complex matrices is essential. A problem encountered when using spectrophotometric methods is interference due to ascorbic acid (AA), often used as an enzyme “protecting agent” during PPO extraction. This study focuses on the nature of AA’s effect on spectrophotometric determinations of PPO activity as well as enzyme extraction. Potato extracts and semi-purified PPO were used as enzyme sources. The inactivation of PPO attributed to AA is substrate-mediated. The extent of AA-dependent inactivation of PPO in model systems varied between substrates. AA only slows mechanism-based inactivation of PPO induced by catechol, possibly owing to the prevention of quinone formation. AA minimally protects PPO activity during enzyme extraction. The problem associated with AA in PPO assay could be circumvented by using ascorbate oxidase to remove AA when catechol is the primary substrate or by using chlorogenic acid as the primary substrate.

The effect of aerosol treatments with calcium-containing preparation on grape quality indicators during long-term storage

В статье представлены результаты применения аэрозольных обработок кальций-содержащим препаратом «Мастер Грин Ca», дана оценка показателей качества винограда в процессе длительного хранении. Исследования проводились в течение 2020 г. в условиях Республики Крым на столовых сортах винограда: Италия, Ред Глоуб, Шоколадный и Молдова. Применение аэрозольных обработок способствовало изменению динамики относительного сахаронакопления сортов Молдова, Ред Глоуб и Италия, к концу хранения массовая концентрация сахаров превышала контрольные значения в диапазоне 3,9-17,6 %. Отмечено снижение активности полифенолоксидазы в опытных вариантах: у сорта Италия после 30 и 90 суток хранения - на 43 и 5 % соответственно, у сорта Ред Глоуб к концу хранения активность снизилась на 40,8 %. Установлено снижение значений естественной убыли массы винограда при применении аэрозольных обработок исследуемым препаратом: у сорта Ред Глоуб - на 44,6 %, у сорта Шоколадный - на 8,5 %, у сортов Молдова и Италия - на 24,4 %. Аэрозольные обработки оказали положительное влияние на органолептические показатели в период хранения, обеспечив гибкость гребня, сохранность естественного окраса, тургора ягод и гармоничности вкуса. Образцы винограда, обработанные препаратом «Мастер Грин Ca», были оценены на уровне 7,71 балла (Ред Глоуб) и 8,93 балла (Италия). The article presents the results of using aerosol treatments with calcium-containing preparation Master Green Ca, the assessment of grape quality indicators in the process of long-term storage is given. The studies were carried out during 2020 in the conditions of the Republic of Crimea on table grapevine cultivars: ‘Italia’, ‘Red Globe’, ‘Shokoladnyi’ and ‘Moldova’. Using of aerosol treatments contributed to changes in dynamics of relative sugar accumulation in the cultivars ‘Moldova’, ‘Red Globe’ and ‘Italia’; by the end of storage, the mass concentration of sugars exceeded the control values in the range of 3.9-17.6%. A decrease in the polyphenol oxidase activity in experimental variants was registered: for the cultivar ‘Italia’ after 30 and 90 days of storage - by 43 and 5%, respectively; for the cultivar ‘Red Globe’ by the end of storage the activity decreased by 40.8%. A decrease in the values of natural loss of grape weight when using aerosol treatments with the studied preparation was established for the cultivars: ‘Red Globe’ - by 44.6%, ‘Shokoladnyi’ - by 8.5%, ‘Moldova’ and ‘Italia’ - by 24.4%. Aerosol treatments had a positive effect on organoleptic characteristics during storage ensuring preservation of stem flexibility, natural color, turgor of berries and balanced flavor. Grape samples treated with Master Green Ca preparation were rated at the level of 7.71 points (‘Red Globe’) and 8.93 points (‘Italia’).