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

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Luisa Pulinas
Carlo Spanu *
Ilenia Idda
Ignazio Ibba
Gavino Nieddu
Salvatore Virdis
Christian Scarano
Francesca Piras
Nadia Spano
Gavino Sanna
Enrico Pietro Luigi De Santis
(*) Corresponding Author:
Carlo Spanu | cspanu@uniss.it

Abstract

The present work was aimed to define and validate farmstead production of lactose- free Pecorino di Osilo cheese, fresh ricotta cheese, and salted and smoked ricotta cheese (Ricotta mustia). 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 unit/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 Pecorino di Osilo cheese. The resulting whey was used to produce fresh ricotta and Ricotta mustia cheese. Raw milk and whey samples were always below lactose detection limit. The residual lactose was measured in Pecorino di Osilo cheese, after 24 hours and 30 days from production; in fresh ricotta cheese, after 48 hours; in Ricotta mustia cheese after 7 days. The determination of lactose content in cheese samples was conducted by a gas chromatography- flame ionization detection method, which showed a LOD and limit of quantification respectively of 1.8 and 5.6 mg/kg for cheese, and 1.35 and 4.2 mg/kg for both ricotta 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 and 11,000±2000 mg/kg in fresh Pecorino di Osilo, 1100±300 and 1200±300 mg/kg in fresh ricotta, and 950±400 and 750±250 mg/kg in Ricotta mustia. The results of the present study showed that the production of farmstead lactose-free Pecorino di Osilo cheese and ricotta 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 hazard-analysis and critical control principles aimed at guaranteeing the effectiveness of the process and at acquiring analytical evidences to demonstrate the fulfilment of law requirements for labelling.

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