## 1 Introduction  
Polyphenols are secondary plant-derived bioactive metabolites [1]. These compounds are able to prevent lipid oxidation, deterioration of polyunsaturated fatty acids and inhibit the growth of undesired pathogenic and spoilage microorganisms in food products [2, 3]. Polyphenols also exert beneficial effects on the human health, including the prevention of different chronic diseases [4]. In the last decades, in light of the directives from the European Commission (1999/31/EC and 2008/98/EC) related to waste and environmental sustainability, fruit and vegetable processing industries have focused their efforts to diminish the environmental impact of wastes and by-products. One promising strategy to valorize these organic matrices is the extraction of active compounds [5, 6]. In this context, particular attention has been paid to vinery by-products [7], in particular grape pomace, which represents approximately 20-25% of the grapes at harvest [8]. Grape pomace contain grape skin and seeds [9] and represents a waste biomass difficult to dispose of [10], since it cannot be directly applied as a soil conditioner or fertilizer due to high levels of phenolic compounds inhibiting the germination of plant seeds [11] and the growth of soil microorganisms [12]. Grape pomace cannot be used in animal feed either because the presence of lignin limits its digestibility [13]. However, due to the increasing consumer request of functional foods [14], grape pomace in powder form, namely grape pomace powder (GPP), has been added to foods containing low levels of polyphenols and dietary fiber in order to improve their functional and nutraceutical properties [15].  
Cheese is consumed almost worldwide and represents an important source of proteins, minerals, vitamins and fatty acids [16], but it is poor in bioactive compounds [17]. The enrichment of cheese with polyphenols has been recognized as a good strategy to produce healthy and functional cheeses [18].  
To this purpose, fruit and vegetables by-products such as artichoke external leaves, broccoli stems and leaves, corn bran, tomato peel [19] and wheat bran [20] have been powdered and used in cheese production. The use of GPP for making dairy products is not new. The addition of GPP in bovine dairy products such as yogurt [21; 22] and semihard and hard cheeses [23] has been investigated and their effect on the nutritional quality of the processed foods evaluated. Very recently, the addition of GPP to fresh ewe's milk cheese has been investigated using single _Lactococcus lactis_ strains at the pilot plant scale level [24], but no industrial production has been carried out. In order to perform high volume cheese production, commercial starter cultures are of paramount importance because they include several mixed-strain starters to overcome phage related issues [25].  
This study is part of a project mainly aimed at finding commercial alternatives for the valorization of ovine cheeses as well as reuse of winemaking industry by-products. With this in mind, the specific objectives of the present work were to: (i) evaluate the in vitro inhibitory activity of GPP against commercial starter culture; (ii) monitor the persistence of GPP during the manufacture of GPP-enriched fresh ovine cheese; (iii) evaluate the total polyphenols content of final cheeses; (iv) evaluate the sensory characteristics of the final cheeses.