Milk characterization for a “high-quality” cappuccino

It is well known that for the preparation of a “high-quality” cappuccino, it is very important the quality of the milk used, but also, the temperature at which the milk is whipped: it should not exceed 70°C otherwise milk takes on a "cooked" flavour due to the "caramelization" of lactose, and the milk proteins undergo a process of denaturation. The denatured proteins bind to the tannic acid present in the espresso forming the "casein tannate", a compound that becomes difficult to digest. For this purpose, the optimum temperature should be around 60°C. This study aims to evaluate the nutritional quality of milk in cappuccinos prepared in different conditions of temperature and injected steam in order to find the optimal conditions for the production of “high-quality” cappuccino and milk-based drinks. In this preliminary study, the thermal stability of caseins and whey proteins, the vitamin content and the activity of some enzymes were evaluated after having treated the milk at the temperatures in which the cappuccino and some milk-based drinks are normally prepared. At this purpose, the milk was subjected to different temperatures (50°C; 55°C; 60°C; 65°C; 70°C; 75°C; 80°C) for different seconds (20"; 30"; 40"; 50"; 60 "). After the thermal treatment, the whey protein and casein protein fraction were purified and then were separately subjected to the 15% SDS-PAGE. The resulting protein bands were analysed by the PDQuest software. On the thermal-treated milk were also determined the activity of lactoperoxidase, alkaline phosphatase and the content of some hydro-soluble vitamins (thiamine, riboflavin, niacin, nicotinic acid, pyridoxine). The activity of lactoperoxidase was determined spectrophotometrically at 436 nm using 0.1 M ABTS and 0.025% H2O2 as substrates in 0.1M phosphate buffer pH 5.5. Alkaline phosphatase activity was also determined by spectrophotometer at 400 nm using p-nitrophenyl phosphate as a substrate in 50 Mm Tris-HCl pH 8.0, 10 mM MgCl2. Vitamin content has been determined by RP-HPLC using a C18 column HiQSil C18 HS, 5 μm, 4.6 mm i.d, 250 mm (Kya Tech Corporation, Tokyo, Japan), connected to a HPLC Agilent 1260 Infinity LC System (Agilent Technologies), according to a protocol from Albalá-Hurtado and co-workers [1]. Quantification was achieved by a calibration curve obtained relating the concentrations (M) of each vitamin standard loaded in the column to the peak area corresponding to each concentration. As regards to the protein fraction, the results indicated that the time and temperature at which the milk is subjected during cappuccino preparation do not affect the stability of caseins and whey proteins. Similarly, the activity of alkaline phosphatase and lactoperoxidase was not affected by the thermal treatment. A different behaviour has been observed towards the vitamins content when the milk is subjected to the temperatures in which the cappuccino is prepared. Thiamine (vitamin B1) was not observed in all milk samples analysed whereas riboflavin (vitamin B2), niacin and nicotinamide content decreased with increasing temperature after just 20 seconds of treatment. The content of pyridoxine did not show any changes with increasing temperature and exposure times. These results indicated that milk proteins do not undergo any denaturation due to the temperatures and times used during the preparation of cappuccino, and this could be due to the very short exposure times, not long enough to induce proteins denaturation. However, the vitamin content is significantly reduced in the cappuccino and some milk-based drinks after the thermal treatments. The same experiments will be repeated using the espresso machine provided by the "Simonelli Group", to check if the temperature and the steam injected by the lance directly into the milk can have a greater impact on the structure of caseins and whey proteins.