Giovanna Contarini

Lactose, galactose and glucose determination in naturally “lactose free” hard cheese: HPAEC-PAD method validation

A chromatographic method by HPAEC-PAD was developed and in-house validated for the quantification of low sugar levels in hard cheese, specifically Grana Padano PDO cheese. Particular attention was paid to the extraction procedure, due to residual microbial and enzymatic activities. Specificity in detection and linearity were verified. Recoveries ranged from 93% for lactose to 98% for glucose and galactose. The obtained LOD and LOQ values were, respectively, 0.25 and 0.41mg/100g for lactose, 0.14 and 0.27mg/100g for galactose, and 0.16 and 0.26mg/100g for glucose. The method was applied to 59 samples of Grana Padano PDO cheese: galactose showed the highest concentration and variability among the samples (1.36±0.89), compared to both lactose (0.45±0.12) and glucose (0.46±0.13). Considering the very low levels of sugars detected, authentic PDO Grana Padano could be safely included in the diet of people suffering from lactose intolerance.

Applicability of Lactococcus hircilactis and Lactococcus laudensis as dairy cultures

The aim of this study was to evaluate whether Lactococcus hircilactis and Lactococcus laudensis can be used as starter cultures. To this end, the two lactococci were characterized for traits of technological and functional interest. Tests in milk included growth at 20, 25, 30, and 37u202f°C, flavor production, antioxidant (AO) activity, folate and exopolysaccharide (EPS) production. At 30u202f°C, which resulted the best growth temperature for both strains, Lc. hircilactis and Lc. laudensis lowered the pH of the milk to 4.8 and 5.5, respectively, after 24u202fh of incubation. Sugar and organic acid composition indicated a higher lactose utilization, coupled with a higher lactate accumulation, by Lc. hircilactis, while galactose was completely consumed by both species. Both strains showed a Cit- phenotype after growth in a selective medium containing citrate as the sole carbon source. Nevertheless, a small amount of citrate was used by both lactococci when grown in milk. The two strains were characterized by a different flavor production, showed high AO activity, and produced small amounts of EPS (~30u202fmg/L). Lactococcus laudensis showed a weak proteolytic activity while Lc. hircilactis was able to accumulate folate at levels four times higher than uninoculated milk. When the two lactococci were tested as starter cultures in small-scale cheesemaking trials, cheeses resulted of satisfying quality and contained amounts of ethanol, acetic acid, diacetyl and acetoin higher than controls, obtained using a commercial culture. The application of Lc. hircilactis and Lc. laudensis as aromatic cultures in cheesemaking is proposed.

Selection of Streptococcus thermophilus strains able to produce exopolysaccharides in milk

A collection of 139 Streptococcus thermophilus strains was genetically screened by PCR targeting some genes involved in exopolysaccharide (EPS) biosynthesis. Twenty-nine strains were found to be PCR positive and were grown in skim milk to highlight their ropy character, that is the ability to efficiently thicken the milk cultures and minimise syneresis. Three strains producing a skim milk culture with apparent viscosities of 275xa0±xa014, 340xa0±xa021 and 510xa0±xa042xa0mPa.s, significantly higher than the average value (135xa0±xa087.3xa0mPa.s), were selected. EPS from milk cultures of these three strains was extracted and quantified from 84.4 to 209.2xa0mg/L.