Constituents of nutritional relevance in fermented milk products commercialised in Italy

Abstract

Fermented milk products represent an increasing share of the dairy products consumed in Italy. The nutritional value of these products is related to the milk utilised and to the eventual presence of other ingredients (milk powder, sugar, fruit puree and fruit extracts), whereas the microrganisms used can affect texture and organoleptic characteristics. In this paper constituents of nutritional relevance such as protein, fat, total carbohydrate, amino acids, minerals, vitamin A, vitamin E and cholesterol, have been evaluated in yoghurts, fermented milks (plain and with essences) and Quark cheeses (plain and with fruits). This study confirms the high nutritional quality of fermented milks and stresses the role of non-milk ingredients in modifying and, sometimes, improving the dietary contribution of these products.

Introduction

The fermentation of milk with lactic acid bacteria leads to peculiar organoleptic characteristics of the final product due to the reduction of the lactose content and, consequently, to the production of lactic acid and the coagulation of milk protein.

A variety of benefits have been associated with lactic acid bacteria. An improvement of calcium bioavailability and lactose digestibility in lactase-deficient individuals (Shermark, Saavedra, Jackson, Huang, Bayless & Perman, 1995), a balancing of the intestinal microflora, a hypothesised hypocolesterolemic effect (Eichholzer & Stahelin, 1993) and a potential prevention of colon cancer (Kampman, Goldbolm, Van Den Brant, & Van't Veer, 1994) are reported in the literature on this subject.

Different lactic bacteria can be utilised in the manufacture of fermented milks but, according to the Codex Alimentarius definition (FAO, 1992) and to the Italian legislation (Ministero Della Sanitá, 1972), the fermented product can be called “yoghurt” only if the bacteria synergically growing in milk are Streptococcus thermophilus (new nomenclature: Streptococcus salivarius ssp. termophilus) and Lactobacillus bulgaricus (new nomenclature: Lactobacillus delbrueckii ssp. bulgaricus).

Traditional yoghurt bacteria do not belong to natural intestinal flora and cannot implant themselves in the intestines, but some selected intestinal bacteria can be isolated and utilised in the manufacture of fermented milks to increase their beneficial role to human health (Rosenthal, 1991).

Recently, fermented products utilising Bifidobacterium and Lactobacillus, that are reported to have health-promoting properties (Gibson & Roberfroid, 1995), have been commercialised. These lactic bacteria are called “probiotics” i.e. “live microfloras which beneficially affect the host animal by improving its intestinal microbial balance” (Fuller, 1989).

Other dairy products, containing living lactic bacteria, can be considered similar to the more traditional fermented milks. In particular, Quark cheese is a fermented product made from skimmed or partially skimmed cow milk previously heat-treated at 70–90°C for a short time and, afterwards, treated with liquid rennet and inoculated with Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. cremori and Lactococcus lactis ssp. diacetylactis. The thermal treatment leads to interactions between casein and whey proteins and a large part of the whey protein co-precipitates with casein on the acidification due to a prolonged incubation with lactic bacteria (Salvatori Del Prato, 1993). Finally the base-product can be treated with other ingredients of different origin such as fruit, vegetable or fish.

In terms of overall composition, all fermented milk products have a nutritional value corresponding to the composition of the milk from which they are made, even though small differences in the concentration of a chemical constituent could be present, due to the manufacture and the fermentation process. The main modifications are: (i) a considerable formation of lactic acid and a consequent decrease of lactose; (ii) an increased content of free molecules, such as small peptides, amino acids and fatty acids. Furthermore, the composition of these products can be also modified and integrated by some ingredients of different origin, such as fruit (puree or pieces) and/or sugar.

In this work we studied, from a nutritional point of view, traditional and innovative fermented milk products such as yoghurt, fermented milks, and Quark cheeses, natural or treated with other ingredients. All these products are well represented in the Italian market and their consumption is increasing due to increased consumer attention. Finally, in homage to tradition, a fermented milk of very ancient origin in Italy (Sardinia) has also been studied. It was traditionally prepared from ewe or goat milk inoculated with a starter culture including bread yeast, a spoon of vinegar and a small quantity of rennet and is called “Gioddu”. Nowadays, Gioddu is industrially produced with homogenized milk, heated at 90°C for 15 min, cooled to 44°C, inoculated with Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus salivarius ssp. termophilus for 4–5 h.

The curd is broken, cooled and packaged. The product is more consistent than yoghurt, has a white and shiny appearance and is rich in aromatic substances.