Technical solutions for better storage of Prickly pear fruit by-products

Take home Message Prickly pear fruit by-products hold promise as an alternative feed source for livestock. Introduction The use of agro-industrial by-products as animal feed represents an important component of the global strategy to reduce the environmental impact of agro-industrial and to increase livestock production. The use of some byproducts as animal feed has been explored and could represent a socio-economic advantage in order to reduce the competition for food directly consumable by humans. By-products are commonly used in the animal feed industry due to their high nutritional value, being rich in fiber or protein, and bioactive molecules. Prickly pear by-product (PPB), obtained from processing of juice extraction of Opuntia ficus-indica (L.) fruits, could be an interesting by-product for ruminant feeding. However, PPB, as several by-products, are subject to seasonality and some of these are difficult to store. This paper reports the results obtained from two preliminary investigations with the aim to enhance the PPB storage aptitude. Material and methods The aim of the first study was to evaluate the nutritional characteristics of PPB and its stability during a 21-days of outdoor storage. The potassium metabisulfite (PMB), as natural stabilizer, was added to the PPB at different doses (0, 50, 100, and 150 g/kg). Samples of treated PPB were analysed at days 1, 3, 7, 14, and 21 for chemical composition and microbiological profile (Todaro et al., 2020). In the second study, PPB was ensiling with different levels of wheat straw (0, 5, and 10% as fed). After 35 days of storage, from 4 micro-silages for each thesis, samples were collected and analysed for composition and fermentation kinetics using the in vitro gas production technique (Vastolo et al., 2020). Results and discussion The fractioning of PPB showed that it contained 28% of peel and pulp and 72% of seeds on a DM basis. This new byproduct is low in moisture and protein when compared to other fresh by-product available in Sicily for ruminant feeding, such as fresh lemon pulp. Overall, PPB was low in crude protein (CP, 5.3% DM), high in fiber (51.4%, 41.2% and 14.6% DM for NDFom, ADFom and ADL, respectively), non-fiber carbohydrates (NFC, 29.7% DM), and soluble sugars (13.3% DM), with a moderate level of net energy for lactation (4.59 MJ/kg DM). In the first study, the storage time was responsible for the decline, during the first week, of NFC and soluble sugars, mainly due to fermentation activity, and then it stopped. The same trend was observed for the pH values during the first week, which subsequently showed a substantial increase at day 21, presumably due to a deacidification following the use of acid lactic for microbial growth. On this basis, the use of PMB at doses of 100 and 150 g/kg was able to slightly slow down the early phase of the acidification process and limit the presence of spoilage microorganisms, coliforms and Enterobacteriaceae after a three-weeks storage period. The second study showed that PPB silage with the addition of wheat straw guaranteed the preservation of NFC and CP, indicating a potential reduction in losses due to leachate. PPB silage showed good ensiling parameters (Table 1), especially when 5% of straw is added: significantly lower pH and ammonia nitrogen concentration. Furthermore, comparing the three PPB silages, the inclusion of 5% of straw seems to guarantee higher fermentability (organic matter disappearance, OMD, and cumulative volume of gas related to incubated organic matter, OMCV) and volatile fatty acids production. Conclusion Prickly pear fruit by-product could be a very interesting diet ingredient for ruminants. PPB seems to be an important nutrients’ resource suitable to increase the economic value and the environmental sustainability of livestock farming as well as giving added value to dairy products. The results obtained with the use of PMB showed that this byproduct is able to control the fermentation process and the presence of alterative microorganisms, but also the difficulty to obtain a homogeneous distribution in the by-product mass. Instead, ensiling PPB with wheat straw is an appropriate storage technique to preserve the nutritional characteristics of PPB. Further studies are necessary to evaluate alternative conservation methods.