The quality, flavor, and texture characteristics of cheese depend on several factors, including milk composition, processing conditions, the type of microorganisms employed, and storage methods. Hard and semi-hard cheeses such as Parmesan, Cheddar, Gouda, and Emmental contain less than 56% moisture and develop a compact texture and rich flavor during long ripening periods. Maintaining the quality and safety of these cheeses requires effective preservation techniques that prevent the growth of harmful microorganisms while retaining beneficial bacterial activity. Therefore, both traditional methods such as salting and modern technologies like active packaging are used to extend shelf life and enhance sensory and environmental stability.
- Growth of Pathogens During Ripening of Hard and Semi-Hard Cheeses
During the ripening of hard and semi-hard cheeses such as Cheddar and Emmental, most pathogens, including E. coli, Salmonella, and S. aureus, gradually decline; however, some, such as Listeria monocytogenes and heat-stable S. aureus toxins, may persist. Factors such as cooking and ripening temperature, and pH levels play a key role in their survival — low temperatures and high pH can favor pathogen persistence. Although current regulations, such as the mandatory 60-day ripening for raw-milk cheeses, aim to ensure safety, evidence suggests these measures are not always sufficient to eliminate all pathogens and may require revision.
- Effect of Storage Methods on Sensory Properties
The flavor and texture of hard and semi-hard cheeses are influenced by storage conditions. Low-temperature freezing can preserve sensory properties, though appropriate packaging is essential to prevent freeze damage. Overall, the optimal storage method depends on three factors: the intended storage duration, and the desired aroma, flavor, and appearance of the cheese at consumption.
- Preservation Methods for Cheese
3.1 Traditional Methods
3.1.1 Ripening
Ripening is a key stage in traditional preservation of hard and semi-hard cheeses, as their long storage periods make them susceptible to spoilage. During maturation, numerous microbial, biochemical, and physicochemical changes occur, contributing to the development of distinctive flavor, texture, and aroma. These transformations are mainly influenced by proteolytic enzymes from starter microflora and milk coagulants. Ripening time varies from 15 to 90 days depending on the cheese type, and precise control of temperature, humidity, pH, and salt is essential for maintaining sensory quality.
3.1.2 Salting
Salting is one of the oldest and most effective traditional methods for preserving hard and semi-hard cheeses. Salt reduces moisture, inhibits spoilage bacteria, and improves flavor and texture. It can be applied either dry or via brine immersion, depending on factors such as brine concentration, curd moisture, and contact surface. Besides suppressing undesirable microbes, salt supports the growth of beneficial bacteria and flavor compound formation. However, reducing salt content is challenging, as it directly affects sensory quality, water activity, pH, and microbial balance — potentially disrupting the delicate equilibrium between flavor, texture, and safety.
3.2 Modern Techniques for Quality Preservation and Shelf-Life Extension
Hard and semi-hard cheeses are vulnerable to microbial spoilage during ripening and storage. To prevent degradation, various techniques are used, including high-pressure processing (HHP), antifungal additives, and microbial control through increased CO₂ levels. Rod-shaped bacteria are more pressure-sensitive than cocci, while endospores are highly resistant. Antifungal agents such as sorbates, benzoates, and natamycin are commonly used to prevent mold contamination.
The cheese microbiota includes two groups: primary starter cultures (lactic acid bacteria, LAB) that initiate fermentation, and secondary microbiota consisting of non-starter LAB, yeasts, and molds. Accurate control of anaerobic microorganisms is essential, as their activity can lead to volatile compounds and undesirable odors.
3.2.1 High-Pressure Processing (HHP)
HHP is an effective non-thermal method for inactivating unwanted microorganisms in hard and semi-hard cheeses without harming beneficial LAB. The process applies uniform pressure (200–600 MPa) for 10–20 minutes at temperatures below 45°C. Studies show HHP significantly reduces Enterobacteriaceae, Listeria innocua, molds, and yeasts without altering cheese flavor, texture, or proteolytic activity. Moreover, it delays lipid oxidation and enzymatic reactions, extending shelf life under refrigeration.
3.2.2 Additives
Antifungal Additives
Natamycin, produced by Streptomyces species, is one of the most widely used antifungal agents in cheese production. Effective at low concentrations (1–20 ppm), it prevents mold and yeast growth without affecting sensory quality. Compared with preservatives such as potassium sorbate or propionic acid, natamycin offers superior efficacy and lower penetration into the cheese matrix. Natural alternatives — essential oils from cinnamon, rosemary, and oregano — are also gaining attention as eco-friendly antifungal agents.
Antibacterial Additives
Antibacterial agents such as lysozyme, potassium sorbate, nisin, nitrates, and propionic acid are applied to control spoilage and pathogenic bacteria during ripening. Lysozyme, a natural enzyme from egg white, prevents late blowing defects caused by Clostridium. Nisin, a bacteriocin produced by Lactococcus lactis, effectively inhibits Gram-positive pathogens like Listeria and is considered a safe, natural preservative. Recently, plant-based extracts from green tea, pomegranate peel, and aromatic herbs have attracted attention for their antimicrobial and antioxidant properties, helping extend shelf life while maintaining sensory attributes.
3.2.3 Salt Content
Salt plays a crucial role in ensuring safety, texture, and shelf life by inhibiting unwanted microbial growth and aiding whey expulsion. In combination with temperature and humidity, salt helps suppress pathogens such as Listeria monocytogenes, Staphylococcus aureus, and Salmonella. However, sodium reduction or substitution (e.g., with potassium) can alter microbial balance, biochemical reactions, and flavor, and increase susceptibility to spoilage organisms like Pseudomonas. Therefore, maintaining optimal salt balance is essential for product safety and quality.
3.2.4 Storage Temperature
Storage temperature strongly affects the safety and quality of semi-hard cheeses. Low or sub-zero storage inhibits microbial growth and extends shelf life for over a year, though requires impermeable packaging to prevent freeze damage. While room temperature accelerates ripening, lower temperatures reduce LAB activity. The optimal storage temperature for semi-hard cheeses is around 10°C. Freezing at −20°C maintains chemical and microbial quality by slowing enzymatic and oxidative reactions, though may cause minor textural changes.
3.2.5 Packaging Technologies
Due to high water activity and moderate acidity, cheese is highly susceptible to microbial contamination. Effective packaging protects against chemical, physical, biochemical, and microbial deterioration. Conventional synthetic films are efficient but environmentally problematic, prompting the development of biodegradable alternatives such as biofilms and bionanocomposites, which offer good oxygen barrier properties but higher permeability than plastics.
Edible Packaging
Edible films and coatings made from polysaccharides, proteins, lipids, and waxes act as semi-permeable barriers against oxygen, CO₂, and moisture loss. They can also carry antimicrobial and antioxidant compounds. Studies show coatings containing chitosan, galactomannan, whey protein isolate, tapioca starch, natamycin, nisin, and plant essential oils reduce mold growth and weight loss while improving texture and sensory quality.
Active Packaging
In active packaging, antimicrobial and antioxidant compounds (e.g., natamycin, silver nanoparticles, lysozyme, essential oils) are incorporated into the film to inhibit microbial growth and extend shelf life. Some films also absorb oxygen or neutralize free radicals, preventing lipid oxidation. Key challenges include stabilizing natural compounds and controlling their release rate.
Intelligent Packaging
Smart packaging uses sensors and indicators (oxygen, time–temperature, colorimetric) to monitor product freshness and detect spoilage. For instance, color or fluorescence-based sensors indicate oxygen depletion or pH shifts, while electronic noses (e-nose) detect volatile compounds to estimate ripeness and freshness.
Modified Atmosphere Packaging (MAP)
MAP alters the gas composition around cheese (typically CO₂, N₂, and sometimes O₂) to inhibit microbial growth and preserve flavor and appearance. CO₂ suppresses spoilage bacteria, while N₂ prevents package collapse, significantly extending shelf life without quality loss.
Vacuum Packaging
Vacuum packaging removes air to inhibit aerobic microorganisms and lipid oxidation, preserving cheese color, flavor, and moisture. Although effective, it may slightly alter texture in some varieties, requiring adaptation to cheese type.
- Application of Artificial Intelligence in Cheese Quality Assessment and Production
Artificial intelligence (AI) has become an emerging tool for improving cheese quality assessment and production efficiency. AI systems can accurately predict shelf life and quality based on parameters such as pH, soluble nitrogen, and microbial counts. Advanced computer vision and machine learning models achieve up to 99% accuracy in evaluating color, texture, structural defects, and ripening stages. By automating quality monitoring, AI reduces human error and enhances consistency, offering a transformative approach to modern cheesemaking.
Conclusion and Future Outlook
Each cheese type requires tailored preservation conditions to maintain its quality and safety. Among innovative methods, high-pressure processing (HHP) demonstrates the greatest industrial potential, either alone or combined with other techniques. Novel packaging systems also play a vital role in improving shelf life and quality control, though further research is needed for large-scale implementation.
Overall, these innovations significantly enhance the longevity of hard and semi-hard cheeses and increase profitability within the dairy industry. Moreover, integrating artificial intelligence into cheese production represents a major step toward precision, efficiency, and sustainability — enabling real-time, non-invasive monitoring of ripening, texture, and composition, reducing waste, and shaping a more sustainable future for the cheese industry.
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