Article pubs.acs.org/JAFC
Coffee Silverskin: Characterization, Possible Uses, and Safety Aspects Tullia Gallina Toschi,†,‡ Vladimiro Cardenia,*,†,‡ Giorgio Bonaga,† Mara Mandrioli,† and Maria Teresa Rodriguez-Estrada†,‡ †
Food Waste Innovation Centre, Department of Agricultural and Food Sciences, Alma Mater Studiorum-Università di Bologna, Viale Fanin 40, 40127 Bologna, Italy ‡ Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum-Università di Bologna, Piazza Goidanich 60, 47521 Cesena (FC), Italy S Supporting Information *
ABSTRACT: The reuse of coffee silverskin (CS), the main waste product of the coffee-roasting industry, could be an alternative to its environmental disposal. However, CS could also contain undesirable compounds, such as ochratoxin A (OTA) and phytosterol oxidation products (POPs). A study on the composition of CS (caffeine, moisture, dietary fibers, carbohydrates, and polyphenol contents) was carried out, with emphasis on OTA and POPs for safety reasons. The lipid fraction showed significant amounts of linoleic acid and phytosterols (7.0 and 12.1% of lipid fraction). Noticeable levels of POPs (114.11 mg/100 g CS) were found, and the phytosterol oxidation rate varied from 27.6 to 48.1%. The OTA content was 18.7−34.4 μg/kg CS, which is about 3 times higher than the European Commission limits for coffee products. The results suggest that CS could be used as a source of cellulose and/or bioactive compounds; however, the contents of POPs and OTA might represent a risk for human safety if intended for human or livestock use. KEYWORDS: coffee silverskin, ochratoxin A, phytosterol oxidation products, lipid content, safety risk
1. INTRODUCTION
circulation in the skin and also stimulates hair growth through inhibition of 5α-reductase activity.14 Due to the interesting CS chemical composition, a demand of its revalorization has lately increased. Many authors1,7−9,15−18 have suggested CS as a natural source of a wide range of compounds (such as polyphenols, dietary fiber, xantine), having positive effects on human health. Furusawa et al.18 investigated the inhibitory effect of CS on hyaluronidase enzyme. Jaquet et al.19 reported an increase of the metabolic activity of Bifidobacterium spp. (prebiotic effect), while Pourfarzad et al.17 suggested the use of CS as an ingredient for the formulation of a dietetic bread (high fiber and low caloric contents). Recently, Martinez-Saez et al.8 prepared an antioxidant beverage with a CS extract to prevent fat accumulation and excess weight, thus confirming its potential for health-promoting applications. However, CS could contain undesirable compounds, such as ochratoxin A (OTA), which has been classified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen (group 2B).20 OTA is produced by Aspergillus ochraceus and Penicillium verrucosum, and tends to bioaccumulate along the food chain; in fact, human exposure occurs by consumption of contaminated raw materials (e.g., food grains) and/or food products (e.g., pork meat products). OTA can induce renal toxicity, nephropathy, and immunosuppression, as reported by Ferraz et al.21 Coffee contamination by fungi occurs when coffee fruits fall onto the soil or during
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Coffee represents one of the most widely consumed beverages and Brazil is the global leader of green coffee production, with 105 million tons per year.2−4 The most important botanical coffee species and varieties are Coffea arabica (Arabica) and Coffea canephora (Robusta), which represent about 75 and 24% of the global production, respectively.5 The coffee beverage is obtained from roasted green coffee. During this technological phase, the characteristic properties of coffee beverage (such as flavor and aroma) are developed, and the remnant thin tegument that covers and protects the outer layer of green coffee bean (coffee silverskin) is removed.6 Additionally, considering that more than 50% of the fruit is discarded,6 coffee production leads to an elevated amount of waste, such as husks or coffee silverskin (CS), of which only a slight percentage is reutilized. Therefore, isolation and valorization of bioactive compounds from the coffee industrial waste could be a possibility to avoid their lost. Caffeine (1,3,7-trimethylxanthine) is the main alkaloid present in green coffee and CS,1,3,6−9 and it is a molecule of great interest for the pharmaceutical, cosmetic10 and food sectors. Caffeine is known for its stimulant properties on the systemic circulation, the respiratory capacity, and the central nervous system, contributing to maintain cognitive functions.11 O’Keefe et al.12 reported that coffee consumption may reduce the risk of type 2 diabetes mellitus and hypertension, as well as other conditions associated with cardiovascular risk; potential protection against neurodegenerative diseases has been also observed. Moreover, the cosmetic industry widely uses caffeine as active ingredient in creams, due to its antioxidant, thermogenic, lipolytic, and UV-ray protection effects.13 Caffeine present in cosmetics also increases blood © XXXX American Chemical Society
Received: July 9, 2014 Revised: October 15, 2014 Accepted: October 16, 2014
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dx.doi.org/10.1021/jf503200z | J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Journal of Agricultural and Food Chemistry
Article
Figure 1. Structures of campesterol, stigmasterol, sitosterol, and their main oxidation products (POPs).
literature. However, in order to propose some reuse of CS, it is of outmost importance to define the potential safety risks. The aim of this paper was to evaluate the CS suitability as possible source of bioactive compounds, as well as the presence of potentially hazardous compounds, in usual storage conditions employed for this waste product. A full characterization study focused on both lipophilic and hydrophilic components of CS was carried out. OTA and POPs were determined, together with the fiber content, the total phenolic compounds, the carbohydrate composition, and the caffeine amount. Different methods for extracting the lipid fraction were tested, and its total fatty acid composition and total PS content were investigated.
storage; in fact, the presence of OTA in green coffee was reported for the first time in 1974,22 and thereafter, many authors have determined the OTA content in green and roasted coffee or in coffee beverages.5,21,23−25 Contradictory results about the effect of roasting on the reduction of OTA in coffee beans have been reported. However, it seems that roasting can diminish OTA content, as reported by Napolitano et al.5 and Romani et al.,23 who observed an OTA reduction >90% in green coffee after roasting. Although the latter could be an effective process for reducing OTA content in coffee, it should be pointed out that roasting conditions (time/temperature) could differently impact OTA destruction. On the other hand, several studies mention physical removal of OTA by elimination of coffee silverskin before and during the roasting process;5 in fact, since CS covers and protects the coffee bean, it is possible that a high amount of OTA is concentrated in CS. Nevertheless, only a few papers reported the presence (
