1. 2. Ambalarea laptelui pasteurizat, ultra-pasteurizat, UHT: parametrii de calitate, reactii de degradare, rolul ambalării în controlul proceselor de degradare, tipuri de ambalaje
2.1. Introducere
Laptele - amestec complex de apă, proteine, lipide, glucide, enzime, vitamine și minerale
Datorită compoziției specifice și a faptului că pH-ul este apropiat de 7, laptele este un aliment perisabil cu potenția ridicat de alterare, ceea ce afectează calitatea și siguranța pentru consumatori
Calitatea laptelui se deteriorează datorită următorilor factori și procese:
lumina și oxigenul care determină procese de foto-oxidare și auto-oxidarea grăsimilor
bacteriile psihro-trofe (care cresc relativ rapid in domeniul temperaturilor comerciale de refigerare) care modifică parametrii organoleptici
- compușii aromatici care se adaugă în diferite etape ale procesării și care pot interacționa cu ambalajul, ducând la modificări nefavorabile de miros a alimentului

2. Siguranța alimentului este afectată de distrugerea incompletă a agenților patogeni care provin de la animal
Ambalarea, ca parte integrantă a operațiilor de procesare a laptelui, oferă:
Izolare
comoditate la manipulare
protecția împotriva: - mediului extern
- factorilor fizici și chimici (lumina, oxigen, vapori de apă)
- pierderilor de componente aromatice dorite (eliminarea aromelor nedorite)
- contaminărilor cu microorganime patogene, insecte, rozătoare, pe durata transportului și depozitării
Un sistem de ambalare eficient trebuie să asigure și alte roluri:
- compatibilitatea cu alimentul
- capacitatea de reutilizare și/sau reciclare
- să conțină particularități anti-fraudă
- să fie netoxic
- aspect atractiv
- prelucrabilitate
- funcționalitate în ceea ce privește forma, dimensiunea și disponibilitatea

3. Tipuri de produse lactate pe bază de lapte:
lapte pasteurizat – dominant
lapte UHT
lapte ultra-pasteurizat (UP)
lapte sterilizat în sticlă
lapte evaporat conservat
lapte cu arome (căpșuni, scorțișoară, cafea...)
lapte microfiltrat și bacterio-steril
Valabilitatea acestor tipuri diferă în fucnție de compoziție, tratarea termică și ambalaj.

4. Aspectele care trebuie luate în considerare la alegerea unui ambalaj sunt:
cunoașterea detaliată a proprietăților alimentului și a mecanismelor proceselor care le deteriorează
valabilitatea dorită
pericolele care apar pe durata transportului
proprietățile ambalajelor
La ambalarea laptelui se pot folosi sticla, metalul, platicele, cartonul, fibrele, compozitele.

5. 2.2 Indicatori de calitate
physicochemical, enzymic, and microbial indices
Physicochemical indices:
pH (6.6–6.8)
titratable acidity (0.14–0.16 % lactic acid)
densitate a laptelui de vacă (1.028–1.035 g / mL) at 15°C
refractive index (1.344–1.349) at 20°C
viscosity (~2 cP (centipoise ) = 2 mPa s at 25°C) (1 cP = 0,001 Pa s = 1 mPa s )
freezing point (–0.53°C to –0.57°C).
Enzymic indices:
alkaline phosphatase - heat sensitive and is inactivated during pasteurization
- absence of alkaline phosphatase is a criterion for
adequate pasteurization
lactoperoxidase - index of milk heat-treated at 78°C for 15 sec for international
commerce
- prin tratare termică, enzima se descompune, iar dacă apare în
laptele analizat, înseamnă că acesta nu a fost tratat
corespunzător

6. Lactoperoxidase is present in fresh raw milk
Bovine milk contains about 30mg/l of lactoperoxidase and the concentration is fairly constant throughout the lactation
Lactoperoxidase has no antibacterial effect on its own but has the ability to oxidise the thiocyanate ion (SCN-) in the presence of hydrogen peroxide (H2O2) (these components also exist naturally in tears, saliva, and gastric juices)
The resulting chemical compound has an antibacterial effect in fresh raw milk
Against some species of normal gut flora such as streptococci and lactobacilli, the resulting compound has a bacteriostatic effect (inhibiting bacterial growth) while it has bactericidal effect (killing bacteria) against some gram-negative bacteria, i.e. Escherichia coli, pseudomonads

7. Microbial indices for UK, for freshly pasteurized milk:
total plate count (30°C for 12 hr) of ≤3 × 104 cfu mL–1
in most of the United States the standard is ≤2 × 104 cfu mL–1
in Greece it is 105 cfu mL–1
The keeping quality
Sensory characteristics related to flavor and appearance:
bland mouth-feel of milk is a consequence of the oil-in water emulsion, whereas the
slightly sweet and salty taste results from the balance between lactose
and milk minerals
aroma is a consequence of a component balance involving a large number of compounds
in trace (carbonyls, lactones, esters, alkanals, sulfur and nitrogen compounds,
aliphatic and aromatic hydrocarbons)
opacity is due to suspended particles of fat, proteins, and certain minerals
color varies from white to yellow according to the carotene content of the fat
skimmed milk is more transparent, with a slightly bluish tint
Homogenization increases the number and total volume of fat globules, and thus
homogenized milk has a whiter color than its unhomogenized counterpart

8. 2.3. Reacții degradative și indicatori de alterare
Pasteurized milk quality deterioration is perceived by the consumer through off-
flavors that may be caused by physico-chemical or microbial changes in the product
Light-induced off-flavors (physicochemical defects) - most common in milk and are attributed to two distinct causes:
- (1) a burnt sunlight flavor, develops during the first 2–3 days of storage and is caused by degradation of sulfur-containing amino acids (methionine) of the whey proteins
- (2) metallic or cardboardy off-flavor (lack of freshness) that develops 2 days later and does not dissipate
- is attributed to light-induced lipid oxidation
- light exposure, especially at wavelengths below 500 nm, also causes destruction of light-sensitive vitamins, mainly riboflavin and
vitamin A

11. The main chemical defect is lipid peroxidation
Unsaturated fatty acids are attacked by free radicals, which is followed by the addition of O2 to form peroxides or hydroperoxides, resulting in the same sensory changes as light-induced oxidation but through a different
Mechanism
The mechanism of light-induced oxidation begins with riboflavin, which acts as photosensitizer.
Riboflavin absorbs photons to form an excited singlet state (1Rib), which by intersystem crossing forms a triplet state (3Rib).
Triplet riboflavin is subsequently deactivated to yield singlet oxygen (1O2), important in protein oxidation (formation of dimethyl-disulfide from methionine) (type II reaction)
Alternatively, singlet oxygen acts as an oxidant to initiate free radical processes by electron transfer and formation of substrate radicals, superoxide anions, or both (type I reaction).

12. FIGURE 5.1 Role of riboflavin as a photosensitizer in the photo-oxidation of milk

13. Microbiological changes involve growth of psychrotrophic bacteria (gram-negative rods such as Pseudomonads and Alcaligenes) as a result of either inadequate pasteurization or post-pasteurization contamination leading to the formation of microbial flavor described as acidic, bitter, fruity, malty, putrid, or unclean.
Campylobacter jejuni causes foodborne (toxiinfecție alim) disease
In one incident, under-processing of milk appeared to be the problem, whereas in another, C. jejuni survived batch pasteurization in a privately operated pasteurization plant in a boarding school.
Yersinia enterocolitica has been implicated in three large-scale outbreaks of illness associated with pasteurized chocolate-flavored milk in the United States. It appeared that the pathogen was introduced with the chocolate syrup added to milk after pasteurization.
Salmonella has also been involved in at least two outbreaks. Both were attributed to contamination of pasteurized milk by raw milk.
Finally, Listeria monocytogenes was the cause of an outbreak (focar) attributed to incorrect application of HTST pasteurization
No correlation was found between the microbial count at the end of shelf life and the sensory quality of the milk
The sensory shelf life of the milk stored in paperboard cartons at 2°C, 5°C, 7°C, 12°C, and 14°C was 15.8, 13.7, 12.3, 4.6, and 3.9 days.

14. 2.4. Rolul ambalajului în controlul proceselor degradative
Packaging can directly influence the development of the off-flavors described earlier (light-induced oxidation, auto-oxidation, and microbial flavors) by protecting the product from light, O2, and microbial cross-contamination
Visible light covers the wavelengths from 380 to 780 nm
Ultraviolet (UV) covers from 280 to 380 nm and is divided into two sub-regions:
UVA (380–320 nm)
UVB (320–280 nm)
Both visible and UV light lead to the degradation of foods in general and of milk and dairy products in particular
In order to adequately protect milk against photo-oxidation, industry has turned to containers that are mostly or totally impermeable to light
for example, LDPE-coated paperboard cartons have an average light transmittance of 4%, opaque HDPE bottles, pigmented (TiO2, green or blue) PET bottles, pigmented plastic pouches
However, the most common HDPE bottles are not pigmented

15. FIGURE 5.2 Spectral transmission curves of milk packaging materials: (1) clear glass, (2) clear PET, (3) pigmented PET, (4) three-layer pigmented high density polyethylene (HDPE), (5) monolayer pigmented HDPE, and (6) coated paperboard carton

16. 2.5. Sticla
Once glass was the predominant package for pasteurized milk
Glass is the most inert of all packaging materials and provides ultimate protection from O2, moisture, and microorganisms
When colored appropriately (blue, amber, green, and, to a lesser degree, white), glass can protect milk from harmful UV light
Sealing (acoperirea) of glass bottles for milk packaging is usually achieved with aluminum foil caps
Disadvantages of glass: fragility and weight
Glass bottles need to be adequately cleaned and sanitized before reuse
Washing: Modern bottle washers have five stages, including pre-rinsing by both
immersion and spray-cleaning with NaOH solution at 62°C
The bottles are then rinsed with water at 49°C and sanitized with a
hypochlorite spray before final rinsing in warm (49°C and 30°C) and cold
water

17. 2.6. Recipientele din plastic
The main plastics used in pasteurized milk packaging are HDPE, PET, polycarbonate (PC), and LDPE.
High Density Polyethylene Bottles (HDPE)
Unpigmented HDPE bottles transmit 58–79% of the incident light in the wavelength range 350–800 nm
Light transmission can be reduced by pigmenting HDPE with TiO2 at 1–2%, producing an opaque bottle
HDPE jugs (căni) are extrusion-blow-molded to provide a thin-walled, lightweight, and tough container
Advantage: capacity of 2 and 4 L sizes makes it more convenient to hold than, for example, paperboard cartons
HDPE bottles are used for pasteurized full-fat, semiskimmed, and skimmed milk.

18. Other Plastic Containers made from HDPE
Multilayer pigmented HDPE (HDPE + 2% TiO2/HDPE + 4% carbon black/HDPE + 2% TiO2)
Monolayer pigmented HDPE (HDPE + 2% TiO2)
Clear PET
Pigmented PET (PET + 2% TiO2)
Visible and UV light absorbers incorporated into polyethylene dairy resin to protect vitamins in milk from photodegradation

19. Poly(ethylene Terephthalate) Bottles
PET bottles are stretch-blow-molded from PET preforms in sizes ranging from 500 mL to 2 L.
They are superior to HDPE bottles in terms of their mechanical and optical properties, their lower flavor scalping potential, and substantially lower gas permeability values
Oxygen transmission rate (OTR) at 4°C/50% relative humidity (RH) of a commercial 600-mL PET bottle is 19 μL / day compared to 390–460 μL / day for a commercial 600-mL HDPE bottle
Due to the almost complete transparency of PET to light, milk bottles are either labeled or, even better, sleeved using thermo-shrinkable polypropylene (PP) labels.
Besides full-fat, semi-skimmed (semi-degresat), and skimmed milk, PET bottles are also used to package flavored milks such as vanilla, chocolate,
and strawberry, cultured milk, and microfiltered milk

20. Clear PET bottles
Green PET bottles
PET + UV blocker
PET + exterior labels
HDPE jugs
Clear LDPE pouches
Cobalt blue PET bottles
Multilayer pigmented gable-top paperboard cartons
Wavelengths higher than 340 mm pass through transparent and opaque plastics such as HDPE, PET, and polystyrene (PS) and through uncolored glass
Colored packaging is capable of partially blocking harmful wavelengths up to 500 nm
The protection provided by colors follows the sequence black (highest), brown, green, blue, red, yellow, uncolored (lowest)

21. Polycarbonate Bottles
PC bottles have a high temperature resistance and high impact strength and clarity, and are currently used for multiuse baby bottles, which are sterilized before each use, as well as for packaging of pasteurized milk in several countries
PC bottles are lightweight, clear, and shatter resistant; do not impart an after-taste to the contents; and are recyclable.
Clear PC, tinted PC, HDPE, and glass returnable (1 gallon) containers are efficient as well as LDPE-coated paperboard cartons for their protection against the development of light-induced flavor and degradation of riboflavin
Migration of the weak estrogen bisphenol A (BPA) from PC bottles into hot water was in the order of 0.2 g / L when the bottles were new and increased to 6–8 g / L after repeated washing

22. Paperboard Laminate Cartons
Are multilayer containers, usually rectangular with a gable top
The material used is paperboard extrusion coated with LDPE on both sides
The thickness of the paperboard is usually 420–490 μm; the thickness of the two LDPE layers is 15–20 μm for the outside layer and 20–40 μm for the inside layer
LDPE is used externally to provide protection from moisture and indirectly for mechanical integrity, and internally it prevents interaction of milk with the paperboard and provides effective heat sealing
Paperboard cartons with and without inner brown pigmentation and plastic pouches with and without black pigmented overwrap
Paperboard with nisin, chitosan, or both with the aid of a binder in an ethylene vinyl acetate (EVA) copolymer and measured microbial load (APC) and yeasts in pasteurized milk. Paperboards that included the combination of nisin and chitosan gave the highest microbial inhibition.

23. Packaging of ULTRAPASTEURIZED AND ULTRA HIGH TEMPERATURE MILK
Paperboard Laminate Cartons
For UHT milk packaging, aluminum foil is added to the conventional LDPE/paperboard/LDPE structure between the paperboard and the internal LDPE layer (LDPE/paperboard/LDPE/alufoil/LDPE/LDPE) to provide the required barrier properties
FIGURE 5.3 Structure of paperboard laminate cartons for ultrapasteurized and UHT milk packaging

24. Plastic Pouches (Sachets)
Aseptic pouches with or without O2-scavenging film for storage at 26°C for 14 weeks
The O2-scavenging film reduces dissolved oxygen content by 23–28% during storage.
Aluminum Cans
Aluminum cans are two-piece metal containers, one piece making up the can body and bottom end and the second piece making up the top end
The interior of aluminum cans is coated with an enamel or lacquer to protect against corrosion
They are used for the packaging of vitamin-fortified milk for youngsters and flavored milk (e.g., coffee, cinnamon, caramel, nut, or vanilla flavors) in 330-mL containers.
The shelf life of such sterilized products is 1 year without refrigeration.