Quick answer
Yes, olives can contain fungi. There are several species of fungi that can grow on or infect olives during growth, harvest, and storage. The most common fungi found on olives include species of Penicillium, Aspergillus, and Alternaria. However, the presence of fungi does not necessarily indicate the olives are unsafe to eat. Proper processing and storage conditions can minimize fungal growth on olives.
Olives are one of the world’s most ancient and beloved fruits, dating back over 8,000 years to ancient civilizations in the Mediterranean region. Today, olives remain a dietary staple in Mediterranean cuisine and culture. The olive tree (Olea europaea) produces fruit that is cultivated for olive oil, table olives, and other products. Table olives are prepared by curing raw olives to remove their natural bitterness, producing edible fruits. Global production of table olives exceeds 2.4 million tons per year.
During growth and post-harvest handling, olives are susceptible to contamination and colonization by various microorganisms, including bacteria, viruses, and fungi. Fungal growth on olives can originate from spores in the air, water, soil, insects, animals, and human contact. Contamination often increases after harvest, as physical damage to olives during harvesting and processing provides entry points for microorganisms. The high nutrient content of olives also promotes microbial growth.
The presence of fungi (molds) on olives can lead to spoilage and safety concerns if not properly controlled. However, many fungi are harmless at certain levels, and some are even used beneficially in olive fermentation and curing processes. Proper agricultural practices, handling procedures, sanitation methods, and storage conditions are important to minimize fungal growth and prevent contamination of olives.
Common olive fungi
Research has identified a range of fungal species that are able to colonize raw or processed olives:
Penicillium
Species of Penicillium are some of the most common fungi associated with olives. They are known as “blue mold” due to the blue-green color of their spores. Penicillium can grow in the orchards, during curing, and on stored olives. Common species include:
– Penicillium digitatum – causes olive green mold, a major post-harvest disease
– Penicillium italicum – causes blue mold rot
– Penicillium expansum
– Penicillium glabrum
– Penicillium chrysogenum
Under favorable conditions (e.g., high humidity, damage to olives), Penicillium molds can spread rapidly and cause decay. P. digitatum is considered one of the most destructive pathogens for olives, capable of damaging entire stocks within days. Proper storage conditions are critical to inhibit Penicillium growth.
Aspergillus
Aspergillus species are commonly isolated from olive fruits. Major species include:
– Aspergillus niger – can discolor olives and produce ochratoxin A, a harmful mycotoxin
– Aspergillus flavus
– Aspergillus terreus
– Aspergillus fumigatus
Aspergillus niger is most prevalent on brine-cured olives. A. flavus and A. parasiticus can produce toxic aflatoxins under certain conditions. Post-harvest control of humidity, temperature, and storage conditions helps minimize Aspergillus contamination.
Alternaria
Alternaria is a genus of fungi that causes black rotten of olives and produces spores appearing black or dark brown. Major species include:
– Alternaria alternata – causes black spot disease on olives
– Alternaria tenuissima
Alternaria growth is favored by high humidity and temperatures around 25°C. Infection can occur in the orchard, during processing and curing, or on stored olives. Careful monitoring for early signs of infection allows for prompt treatment to control spread.
Other olive fungi
Additional fungi that may be present on olives include:
– Botrytis cinerea – causes gray mold rot
– Mucor racemosus / Mucor circinelloides – can contribute to olive fermentation but also cause spoilage
– Rhizopus stolonifer – causes black rot, soft rot
– Colletotrichum gloeosporioides – anthracnose fruit rot
– Phoma spp.
– Fusarium spp.
– Verticillium dahliae – causes verticillium wilt in olive trees
Yeasts such as Candida, Cryptococcus, Rhodotorula, Saccharomyces, Pichia, and Hanseniaspora may also be present and contribute beneficially to olive fermentation or negatively to spoilage under certain conditions. Proper olive handling and curing provides conditions that favor growth of desirable microbes over fungi that cause defects.
Fungal growth on olives
Fungi can infect olives at various stages:
In the orchard
Spores of fungi may be present in the orchard environment and can infect olives through openings in the olive skin, such as wounds or punctures from insects. Fungal diseases such as sooty mold, olive knot, verticillium wilt, and anthracnose can affect olive trees and developing fruit in orchards, requiring treatment. Good agricultural practices help minimize fungal diseases in orchards.
During harvest
Physical damage to olives during harvesting, such as bruising, scraping, or cuts, provides entry points for fungal contamination. Contact with contaminated harvesting tools, containers, or equipment can also introduce fungi. Careful handling methods reduce olive injuries and opportunities for fungal infection during harvest.
During processing and curing
Fungi may contaminate olives during various stages of processing and curing (fermentation). Tanks, equipment, and tools used for washing, brining, and fermenting olives should be sanitized to prevent contamination. Damage to olive skin in processing further enables fungal growth. Proper curing conditions discourage growth of fungi while promoting desirable fermentation microbes.
During storage and distribution
Freshly processed olives are highly perishable and susceptible to fungal contamination in storage and transport if not properly handled. Factors like temperature, humidity, gas composition, cleanliness and microbial load of storage environments influence potential fungal growth. Cold storage inhibits fungi but chilling injury can increase olive susceptibility. Modified atmosphere packaging helps control fungi. Strict controls in storage facilities prevent spread of fungi on stored olives.
Signs of fungal infection
Visible signs that may indicate fungal contamination of olives:
– Colored mold growth (green, blue, gray, black)
– White filamentous hyphal growth
– Soft, watery olive tissues
– Pitting, lesions or spots on olives
– Shriveling or wrinkling of olives
– Decaying olive flesh
– Off odors
Rapid or abnormal fermentation, gas pockets, high viscosity, or moldy films in brines may also signal fungal infection. Indicator tests can detect presence of fungi and toxins in olive products. Regular inspection, microbiological testing, and analysis help monitor for fungal issues.
Preventing fungal growth on olives
Proper handling at all stages is important to prevent fungal issues with olives:
In the orchard
– Monitor trees for fungal diseases and treat as needed
– Prune trees to increase airflow and reduce fungus growth
– Remove fallen or spoiled fruit promptly
– Disinfect pruning tools between trees
During harvest
– Pick olives carefully to avoid bruises, cuts, and injury
– Use clean harvesting tools and containers
– Transport olives to processing facility quickly after harvest
During processing
– Clean and sanitize all equipment and tanks thoroughly
– Monitor brine acidity, temperature, and fermentation
– Remove damaged or bruised olives
– Use antibacterial washes if needed
During curing
– Maintain ideal brine salinity, pH, and temperature
– Ensure containers are fully immersed in brine
– Test and adjust conditions regularly
– Discard abnormal batches immediately
During storage
– Clean storage areas thoroughly before use
– Maintain proper temperature and humidity
– Use modified atmosphere packaging if appropriate
– Inspect olives and containers regularly for any fungal growth
– Follow first-in-first-out inventory system
Proper facility sanitation, process controls, and employee training in food safety practices are also important to prevent fungal issues at all steps.
Treating fungal contamination of olives
If fungi are detected on olives, possible treatment options include:
– Sorting out visibly contaminated olives
– Increasing acidity of brines to inhibit fungi
– Introducing organic acids or antagonistic yeasts into brines
– Applying fungicidal washes, e.g. acetic acid, sorbic acid, sodium benzoate
– Using protective edible film coatings on olives
– Packaging olives in anti-fungal wrappers
– Controlling storage temperature and humidity
– Discarding extensively contaminated batches
Preventative measures are more effective than treating established fungal growth. Once fungi have caused significant decomposition, the affected olives are typically too hazardous to consume.
Safety of olives with fungi
The safety of olives containing fungi depends on:
– Type of fungi present
– Level of contamination
– Olive variety and style (fresh, cured)
– Processing method
– Storage conditions
– Handling practices
Some key considerations regarding fungi and olive safety:
– Penicillium, Aspergillus, and Alternaria species are common but not highly hazardous at low levels.
– Aflatoxin-producing Aspergillus species are more concerning but rare on properly handled olives.
– Levels below food safety limits may be acceptable, depending on use of olives.
– Fungi growth is more common on damaged, bruised, or improperly stored olives.
– Fresh untreated olives are more prone to fungi than cured olives in brines.
– Prolonged storage increases risk of fungi and associated toxins.
– Good agricultural, handling, and storage practices reduce risk.
– Discarding moldy olives reduces risk of illness.
– Immunocompromised individuals may be at higher risk from fungi.
– Cooking olives can inactivate fungi and toxins.
Overall, properly processed and handled olives with low fungal counts within standard limits can be safely consumed, especially if olives are cooked prior to eating. Good practices minimize fungal issues.
Conclusion
In summary, the presence of fungi on olives is common but controllable with proper agricultural, handling, processing, and storage methods. Penicillium, Aspergillus, and Alternaria species are the most prevalent olive fungi. While low levels of fungal contamination are often safe, heavy fungal growth can render olives unsuitable and hazardous for consumption. Care should be taken to minimize physical damage to olives, sanitize equipment, monitor curing and storage conditions, and inspect regularly for signs of fungal infection. With appropriate controls, the majority of table olives can be protected from excessive fungal growth and safely enjoyed.