Production of farmstead lactose-free Pecorino di Osilo and ricotta cheeses from sheep’s milk

Abstract

The present work was aimed to define and validate farmstead production of lactose-free <em>Pecorino di Osilo</em> cheese, fresh <em>ricotta</em> cheese, salted and smoked <em>ricotta</em> cheese (<em>Ricotta mustia</em>). The enzymatic activity of the commercial preparation containing lactase (1.1 g/mL), preliminarily tested using a spectrophotometric titration, showed activity equal to 4950±40 Neutral Lactase Units/g. The amount of lactase required to obtain the lactose-free milk was then established in triplicate laboratory trials, by adding the enzyme at concentrations of 0.7, 0.9 and 1.1 g/L in flasks containing 160 mL of raw sheep’s milk. Samples were incubated under conditions expected during milk storage and cheese-making. The residual lactose content in milk was determined by enzymatic method. The addition of lactase at concentration of 1.1 g/L of milk reduced the lactose concentration below the limit of detection (LOD) of 0.06 g/L. The procedure was validated at a dairy farm, using three different batches of bulk raw sheep's lactose-free milk that were transformed into <em>Pecorino di Osilo</em> cheese. The resulting whey was used to produce fresh <em>ricotta</em> and <em>Ricotta mustia</em> cheese. Raw milk and whey samples were always below lactose detection limit. The residual lactose was measured in <em>Pecorino di Osilo</em> cheese, after 24 hours and 30 days from production; in fresh <em>ricotta</em> cheese, after 48 hours; in 2 <em>Ricotta mustia</em> cheese after 7 days. The determination of lactose content in cheese samples was conducted by a GC-FID method, which showed a LOD and limit of quantification (LOQ) respectively of 1.8 and 5.6 mg/kg for cheese, and 1.35 and 4.2 mg/kg for both <em>ricotta</em> cheeses. The lactose concentration was always below the relevant LOD values in all samples. The mean concentration of galactose and glucose were respectively 13,000±2000 mg/kg and 11,000±2000 mg/kg in fresh <em>Pecorino di Osilo</em>, 1100±300 mg/kg and 1200±300 mg/kg in fresh <em>ricotta</em> and 950±400 mg/kg and 750±250 mg/kg in <em>Ricotta mustia</em>. The results of the present study showed that the production of farmstead lactose-free <em>Pecorino di Osilo</em> cheese and <em>ricotta</em> cheeses from raw sheep’s milk is easily achievable. The main issue for farmstead production of artisanal lactose-free products is the implementation of permanent procedures based on HACCP principles aimed to guarantee the effectiveness of the process and to acquire analytical evidences to demonstrate the fulfilment of law requirements for labelling.