# Sea Buckthorn Leaves as a Potential Source of Antioxidant Substances
## 3 Results and Discussion
PACs have attracted increasing amounts of attention in the fields of nutrition and medicine because of their various bioactivities, such as their antioxidant, anti-diabetic, anti-obesity, anticancer, anti-inflammatory, and cardioprotective effects [63; 64]. SBT leaves are a rich source of PACs, and indeed, the highest amount of these compounds was found in SBT leaves from the 2016 growing season (18.517 mg/1 g DM). Although the leaves of the tested cultivars did not differ statistically in their PAC content, a trend towards a slightly higher content level of these compounds can be observed in the leaves of the Habego cv. (14.547 mg/1 g DM). Recent years have provided evidence that PACs are present in the extracts of various plants and have antimicrobial potential, including antifungal effects. For example, [PERSON] et al. [65] evaluated the effect of proanthocyanidin polymeric fractions from _Stryphnodendron adstringens_ and successfully showed the inhibition of _Candida albican_ (ATCC 10231) planktonic growth and biofilm development. According to the study of [PERSON] et al. [66] and [PERSON] et al. [67], sea buckthorn seeds contain a substantial number of PACs, but little is known about their antimicrobial activity. SBT twigs, previously regarded as a by-product, were shown to be also a valuable source of substances with promising antimicrobial activity. [PERSON] et al. [9] reported that SBT-derived twig and leaf extracts rich in PACs exhibit antifungal activity and affect important _Candida_ virulence factors, thus having good potential for the development of novel antifungal products supporting traditionally used drugs. From the point of view of the nutritional properties of the raw material, it is also important to bear the interaction of PACs with proteins in mind, especially those rich in proline. The authors of this study found an average of 4 g of proline in 100 g of SBT leaf protein in the raw material assessed, which represents only 5.28% of the sum of all 20 amino acids determined (unpublished data). Biologically important effects of this interaction include blocking the activity of enzymes, particularly proteolytic enzymes. Another effect of the presence of PACs may be to reduce the bioavailability of certain minerals. Another group of phenolic compounds labelled in SBT leaves were anthocyanins, which also have diverse effects, including antioxidant, antimutagenic, anti-inflammatory, and anticancer activity [68]. They are mainly found in berries and give the fruit attractive colours. Berries such as cranberries, bilberries, raspberries, strawberries, grapes, elderberries, and blueberries have the highest anthocyanin content and antioxidant activity. Their presence in other plant species (including other morphological parts of plants), which have not been previously identified, is also highlighted. The leaves from many species are remarkably polymorphic for anthocyanin expression [69]. For example, the yarn, in addition to the edible root tuber, also has edible leaves and above-ground shoots, which contain numerous polyphenolic compounds and, among others, anthocyanins [70; 71]. The anthocyanin content of the SBT leaves studied ranged from 6.375 to 10.928 mg/g DM, confirming, at the same time, the variation in their content in the raw material depending on the year of harvest (\(p\) = 0.004). The content of these compounds in the leaves of the cultivars tested was not statistically differentiated (\(p\) = 0.430), although the leaves of the Ascola cv. tended to have a slightly higher concentration of this component (9.202 mg/g DM). Many studies have investigated the anthocyanin content of the fruit. It should be noted that their content depends on the colour of the fruit. For example, relatively red berries were found to contain more anthocyanins than yellow and light-yellow berries [72]. A qualitative assessment of flavonoids was also made by determining the amount of rutoside and quercetin in SBT leaves (Table 5).