Antioxidant capacity and related parameters of different fruit formulations

Abstract

Fruits and vegetables are known as good sources of phytochemicals, essential to prevent degenerative diseases like cancer and cardiovascular diseases (CVD). They contain a variety of antioxidants, which are useful to scavenge radical oxygen species (ROS). Besides smoothies, fruit purees, concentrates and juices – used by the food industry for these new beverages – were analysed. Total phenolics by Folin-Ciocalteu method, vitamin C content and antioxidant capacity (AOC) by FRAP, TEAC and ORAC assay were analysed by using high-throughput methods on a microplate reader. Vitamin C content ranged from 31 ± 3 mg/100 g in drinkable pomegranate concentrate to 1373 ± 125 mg/100 g in acerola puree; total phenolics content was quantified between 51 ± 1 mg gallic acid equivalents (GAE)/100 g in the mango-peach smoothie and 1152 ± 62 mg/100 g in the ascorbic acid rich acerola puree. The AOC differed depending on kind of fruit and antioxidant assay used. In most fruit products the major portion of AOC was generated by polyphenolic compounds, except acerola puree and orange juice. Very good correlations between total phenolics content and antioxidant capacity were found in the single fruit products, however not in the fruit and vegetable smoothies. Most of the analysed smoothies were able to supply with one package nearly the recommended dietary intake (RDI) of vitamin C for adults of 100 mg per day.

Introduction

Fruits and vegetables are one essential part of human nutrition (Boeing et al., 2007). Especially the large amount of micronutrients makes them valuable in terms of nutritional physiology. They are rich in water-soluble vitamins (vitamin C, B-vitamins), provitamin A, phytosterols (which lead to a lower risk of arteriosclerosis) and show a high variety on minerals and phytochemicals (Gebbers, 2007). Numerous studies have documented the prevention of certain chronical diseases, e.g. hypertension (Dauchet et al., 2007), coronary heart diseases (Dauchet et al., 2006, He et al., 2007), and the risk of stroke (Dauchet et al., 2005, He et al., 2006) by consuming an adequate amount of fruits and vegetables. These diseases are still responsible for the highest mortality rate in Western countries, such as Germany (DeStatis, 2008). Furthermore, polyphenolic compounds such as tea flavonoids (Stoner & Mukhtar, 1995), oligomeric procyanidins (Gerhäuser, 2008), and anthocyanins (Wang & Stoner, 2008) are implicated in the prevention of cancer.

The daily uptake of fruits and vegetables was estimated to be lower than the recommended dietary intake (RDI), advised by the German Nutrition Society (DGE), of 650 g (250 g fruits, 400 g vegetables), especially for vegetables (Max-Rubner-Institut, 2008). To increase the consumption of fruits and vegetables, Germany started the campaign “5 a day” on the basis of the American one initiated by the National Cancer Institute (Rechkemmer, 2002). To increase the intake of phytochemicals, the food industry offers smoothies as an alternative and/or addition to the consumption of fresh fruits and vegetables. Smoothies belong to fruit juices and this term is used since 70 years, primarily in the USA and UK, recently also in Germany. Their production is based on the usage of the total fruits, which are processed to pulp or puree, partially with pieces. Seeds and peel are removed (Qian, 2006). To create different flavours and to allow a drinkable texture, corresponding fruit juices are used. Smoothies are characterised by a high nutrient concentration with low energy content (Watzl, 2008).

Phytochemicals – widely distributed in fruits, vegetables, and their products – possess a high antioxidative potential in vitro. They are able to scavenge radical oxygen species (ROS), and consequently to reduce oxidative cell damages (Spormann et al., 2008). Various methods have been developed to measure the antioxidant capacity (AOC) of fruits and vegetables, but results usually depend upon the type of product and method used (Perez-Jimenez et al., 2008). Due to the differences between the test systems and product characters it is recommended to use at least two methods to measure AOC in any given sample (Schlesier, Harwat, Böhm, & Bitsch, 2002).

The aim of this study was to analyse the antioxidant capacities of a variety of commercially available smoothies as well as of fruit purees, concentrates and juices by using different assay systems. Results were analysed on correlations with contents of total phenolics and vitamin C.