Pomace is a waste material of juice production and mainly consists of stems, peels and kernels. Pomace still holds many valuable nutrients, such as e.g. antioxidants. Antioxidants are substances, which are able to protect cells from oxidative stress, which is why they are often added to food as well as cosmetic products. Consequently, the extraction of these compounds for use in other products would be favourable. Retrieval of antioxidants from pomace can however prove to be challenging because structural elements in plants, such as e.g. cellulose and pectinase, can decrease the extractability of these substances. This is why a research project was conducted to investigate to what extent structural elements inhibit antioxidant extraction from pomace and how enzymatic degradation of said structural elements influences the extractability of antioxidants. Additionally, differences between pomaces of hard (e.g. carrots and apples) and soft (e.g. aronia and currant) fruits were examined.
Over the course of the project apple, aronia, carrot, currant and grape pomace was investigated (see figure 1). Antioxidants were extracted from pomace with and without enzymes, which break down structural elements. More precisely, pectinase was used as an enzyme. Additionally, the amount of structural elements was measured as well. As expected, apple and carrot pomace had the highest and aronia and currant the lowest amount of the structural element pectin. Grape pomace showed a mid-rage amount of pectin.
The amount of antioxidants was determined using a colorimetric method. Therefore, the colour intensity of a blue complex formed by antioxidants and an additive was measured (see figure 2). The more intense the colour, the more antioxidants were in the extract. The results of the extraction experiments showed that overall aronia and grape pomace hold the highest amount of antioxidants, while apple and carrot pomace hold the least (see figure 3). Furthermore, aronia and grape pomace contained a substantial amount of organic pigments. The degradation of structural elements lead to higher antioxidant extractability for all pomaces, but in currant this effect was especially pronounced. It was possible to extract twice the amount of antioxidants from currant pomace with the help of pectinase. Consequently, structural elements strongly inhibit extraction of antioxidants in this pomace. It might even be the case that antioxidants interact with structural elements, which further hinders their retrieval. Carrot pomace on the other hand showed the smallest increase in extractability after use of enzymes. Carrot pomace contains a high amount of structural elements, however, only a small amount of antioxidants. Furthermore, a majority of antioxidants in carrots are carotenoids, which are usually located in the outer layers of the plant, which is why their extraction is most likely not hindered by structural elements.
In a next step, the project aims at investigating the influence of degradation of other structural elements, such as cellulose on the extractability of antioxidants. It will be examined if only the amount of structural elements or type of structural element as well influences the extractability of antioxidants from various pomaces.
This project was funded by the Tiroler Wissenschaftsfond (title: Pomace as a source for micronutrients).
For further information, please get in touch with:
Verena Wiedemair Teaching & Research AssistantDepartment of Food Technology & Nutrition +43 512 2070 – 3827 verena.wiedemair@mci.edu
Fig. 1: Pomaces. From the top clockwise: grape, carrot, currant, apple, aronia pomace. © MCI/Wiedemair.
Fig. 2: Colored complex of antioxidants in varying concentrations. © MCI/Wiedemair.
Fig. 3: Amount of antioxidants in various pomaces. © MCI/Wiedemair.
