Research progress in nutritional components and determination of antioxidant activity in fruits of Prunus

Abstract：Plums belong to genus Prunus of Rosaceae family, which also includes peaches, apricots, and nectarines. Plums are juicy and delicious fruits. Plum fruits have diverse colors and shapes with over 2 000 different varieties and are grown widely. The cultivation area in China is 165 hectares, the second after apple. Around the world there are about 30 species of plums, and in China there are 8 species, including P. salicina, P. simonii, P. domesitica, P. americana, P. nigra, P. cerasifera, P. ussuriensis and P. spinosa. Among the 8 species, P. salicina, P. simonii, P. domesitica and some varieties of P. cerasifera can be cultivated. Fruits of P. salicina are beautiful, aromatic, juicy, mild sweet and sour, and are rich in nutrients. Therefore, P. salicina is most widely cultivated in China. China is the leading harvester of plums, followed by the United States, Serbia, and Romania. People have increasing interests in food nutrients and health function nowadays. Plum fruits have rich necessary nutrients, which are of health and medical functions. Plums contain an assortment of healthy components, vitamins and minerals.Plums are excellent sources of vitamins such as vitamin A, C (ascorbic acid) , folate and vitamin K (phylloquinone) . They are also a good source of vitamin B1 (thiamine) , B2 (riboflavin) , B3 (niacin) , B6 and vitamin E (alpha-tocopherol) . The minerals present in plums include potassium, fluoride, phosphorous, magnesium, iron, calcium and zinc. Plums have rich antioxidant phenols, which have stronger iron absorption and an antioxidant capacity higher than vitamin C. Plums can also normalize blood sugar lev-els and help with weight loss, and the edible fiber in the fruits is good for regulation of cholesterol and intestinal protection. Comparing to other fruits, plums have higher contents of vitamin C, dietary fiber and total phenolic, as well as a higher antioxidant activity. Because of the richness of nutrient components and disease preventing effects, there has been great interest in evaluating the antioxidant activity in plums. Phenols in plums are mainly hydroxycinnamic acid derivatives, neochlorogenic acid, chlorogenic acid and flavan-3-ols. It has been found that total antioxidant capacity (TAC) had a significant correlation with total phenolic content (TPC) . Antioxidant capacity differs among different plum cultivars.There are also differences in antioxidant capacity among different tissues and flesh with different colors. The determination methods for antioxidant activity include the hydrogen atom transfer (HAT) and the single electron transfer (SET) . HAT methods include ORAC (oxygen radical absorbance capacity) and TRAP (total peroxyl radical-trapping antioxidant parameter assay) . While SET methods include DPPH (2, 2-diphenyl-1-picrylhydrazyl radical scavenging capacity) , ABTS (Trolox equivalent antioxidant capacity) and FRAP (ferric ion reducing antioxidant power) . All these methods have their advantages and disadvantages. DPPH is quick and easy but poor in accuracy, because it is susceptible to interference by various reductants that can be reactive with DPPH. ABTS is easy and can be applied to a large number of samples, while its disadvantage are that it is not physiological free radical and lacks of physiological correlation. The reaction time is different with different oxidants; therefore, it provides only qualitative analysis rather than quantitative analysis. FRAP are also easy and can be applied to large amount of samples, but this method determinates the capacity to reduce Fe3+to Fe2+, and therefore the results can not reveal the physiological correlation of the oxidant capacity. On the other hand, different substances have different reactive time, which will greatly influence the results. ORAC are also easy assay and can be applied to high throughput screening and conduct normal quality control, but it is expensive, time consuming and hard to manipulate. Besides, there has been not a standard for evaluating the antioxidant capacity by now. Therefore, researchers usually take 2 or more methods to evaluate the antioxitant capacity at the same time. In this paper, we reviewed antioxidant level and evaluate methods of plums in China and around the world.