Appunti quality and functionality of milk and dairy products

STERILIZED UHT MILK

Definition of UHT treatment by regulation (EC) n.2074\2005: ultra-high temperature treatment is achieved:

• Involving a continuous flow of heat at a high temperature for a short time (not less than 135°C in combination with a suitable holding time) such that there are no viable microorganisms or spores capable of growing in the treated product when kept in an aseptic closed container at ambient temperature
• And sufficient to ensure that the products remain microbiologically stable after incubating for 15 days at 30°C in closed package or for 7 days at 55°C in closed package or after any other method demonstrating that the appropriate heat treatment has been applied.

Both conditions must be met. There’s no upper limit about heat treatment, no quality and genuineness parameters and no official control methods.

Significance of UHT treatment:

• Time \ temperature combination (raw material of poor hygienic-sanitary quality)
• Excessive recirculation of milk

phase of Maillard reaction. It is also a marker of the level of recirculated milk in the plant.

Coupling of lactulose, furosine and GAP: lactulose is a well-known indicator for assessing the severity of athermal treatment but is the most reliable index being not affected by room storage conditions (doesn’t distinguish criterion among different types of sterilized milks). So, the combination of different indicators would provide a better characterization: the level of FUR) could be coupled with LCT content for characterizing genuineness and quality of sterilized milk. While, GAP has been recently proposed as a useful index to evaluate the extent of the advanced stage of Maillard reaction in drinking milk.

This study considers industrial plants (direct and indirect heating) and pilot plant (indirect heating). In both plants the effects of severe sterilization conditions, different proportions of milk recirculation and storage of the finished product have been studied on the levels of the

above molecules in UHT milk.- Industrial plants: nine direct and three indirect UHT milk samples were processed under known different conditions. In two samples of direct treatments, that consist in the higher temperature and the longer holding time, LCT contents was higher than those found for indirect treatments (lower time). Furthermore, these samples do not fit the correlation between LCT and FUR as this last molecule is partly converted into GAP due to the severe heating (in fact, in general, high value of GAP are due to unjustified overheating or excessive proportion of milk recirculation).

A sample of sterilized milk (with UHT) was recirculated with raw milk (so, 10% of UHT milk + raw milk): it is result an higher heat damage (content of LCT increases by 30% and that of FUR by 20%). The double sterilization should be regarded as illegal in UHT milk processing because it is in contrast with recommendation and lead to a drop in quality, but it is possible to minimize the proportion of

When milk recirculation is set at 60%, an increase of all the parameters have been demonstrated.

In the second trial, the prolonged holding time caused the fact that LCT and FUR levels don't fit the correlation.

Lastly, the third trial shows a higher level of GAP, demonstrating that during storage the Maillard reaction proceeds, while FUR levels are lower (the preliminary storage period at room temperature caused the Maillard reaction to move faster towards the advanced stage) and LCT/FUR ratio decreases when reconstituted milk powder is added to milk prior to heat treatment or when the milk is submitted to inadequate storage.

Analytical method

Lactulose

Liquid chromatography (Standard ISO 11868:2007)

Starts with the separation of protein and fat from milk (with chromatography) and proceed with a filtration.

Then, liquid chromatography is applied: the passage through the mobile phase occurs by force of gravity (for others chromatography a determinate pressure is used).

Chromatographic

conditions:- 2 colums in series (aminex 87 P)- Isocratic eluition: water- Detection by refractive index detector (UV detection at 257 nm)- Quantification by external standardization of lactulose by sinthesys.

GapHPLCMilk is subjected to acidification to pH = 4.60 with HCl. Acid whey is obtained and SE on C18 cartridge isapplied. The chromatography conditions are the same as reported for lactulose determination.

CHEESE GENUINENESSBy Regio D.L: n. 2333\1925 cheese is the “product obtained from whole milk or partially or totally skimmedmilk, or from cream, as a result of acid or rennet coagulation, also making use of ferments and salt”.- The name "pecorino cheese" is reserved for products made exclusively from sheep’s milk. If other milksare used, the term "cheese" must be accompanied by the species from which the milk comes- Where cheese is produced exclusively from milk, rennet, salt, enzymes or cultures of micro-organisms,no indication of the

ingredients is required (excluding fresh and processed cheese, for which the label must indicate the salt)- If it has fat referring to dry matter < 35%, the sales name must be completed with the term "lean" (fat <20%) or "light" (fat 20-35%)- Spun fresh cheeses are the only cheeses that must be placed on the market in advance. Only in the case of direct sale in the production dairy is the sale of the pre-paid product allowed.

Raw materials other than milk

• Skim milk powder
• Powdered or concentrated butter milk
• Caseins and caseinates: obtained from milk by acidification or coagulation (rennet casein), solubilized at pH=7 (caseinates) and spray-dried
• Milk proteins (MPC): obtained from milk by ultrafiltration and spray-dried
• Microparticulate whey proteins: obtained from whey by ultrafiltration, thermal denaturation of whey proteins and subsequent mechanical treatment. It is used as a fat replacer, in fact it provides standardization of the protein content of cheesemilk

Law n. 138\1974: the possession, marketing and use of powdered milk and milk preserved with any chemical treatment, or however concentrated, for the production of UHT milk and dairy products are forbidden. The Italian position has been reconfirmed by law decree n. 175 of 08/10/11 with the implementation of EU directive 2007/61/CE regarding certain types of partially or totally dehydrated preserved milk intended for human consumption.

Process to obtain some raw materials:

• Milk is subjected to a pre-heating and then to concentration. After this phase there is evaporation or ultrafiltration followed by drying. Then, milk powder and milk protein concentrate (MPC) are obtained.
• Milk is subjected to heat treatment and then to acidification that permits to precipitate the lactose. There is now a neutralization phase followed by drying to obtain acid casein and caseinates.

So, the production of milk powder and milk protein powders involves the yield increase, and reduction of production costs.

Adoption of heat treatment conditions (two first treatments and evaporation and drying) that results in thermal damage reactions of proteins and sugars. In fact, in presence of lactose (production of milk powders) furosine is produced; while in absence of lactose (production of caseins and caseinates), lysinoalanine is produced. Lastly, in presence of variable lactose content (production of MPC), both compounds are produced.

Furosine (FUR) and lysinoalanine (LAL)

Serine, cysteine and phosphoserine can be dehydrated (from the CH3OH the OH group goes), leaving a compound called dehydralanine, which has a double bond. Dehydralanine is very reactive and can react with lysine from another polypeptide chain to form lysinealanine. This can be used as a heat damage marker.

Study in which casein, caseinate and MPC powders were the samples: the levels of FUR in the experimental casein, caseinate and MPC powders ranged from 5.6 to 427 mg/100 g of protein, whereas the LAL levels varied from 0.4 to 35.2

mg/100 g of protein.In addition to the intensity of the heat treatments adopted during manufacturing, the levels of LAL and FURin this type of products are inversely influenced by the presence of lactose (the residual lactose content inthe powder depends on the effectiveness of the washing or diafiltration steps of the protein fractionisolated from the milk 9): the presence of reducing sugars (so in acid conditions) cause the Maillardreaction to prevail upon β-elimination, with the consequent formation of high levels of FUR and low levelsof LAL. However, the alkaline conditions encountered during heat treatments promote β-eliminationreactions; thus, relatively high levels of LAL are expected when neutralisation or no acidification steps areapplied during the manufacturing of milk protein powders. In this regard, it must also be considered thatthe formation of lactulosyl lysine is not significantly affected by pH, as the early stage of the Maillardreaction is not pH dependent.Consequently,

In addition to the extent of protein glycation and cross-linking phenomena,