Is pumpkin preserves made from real pumpkins

Microbial spoilage of plant foods. Amal vetch

Transcript

1 Microbial spoilage of plant-based foods Microbial spoilage of fresh fruit and vegetables Amal Wicke State Office for Consumer Protection Saxony-Anhalt Halle lecture afternoon

2 Main topics 1. Influences on the microflora of the plants 2. Causes of spoilage 3. Forms of microbiological spoilage 4. Significance of molds as spoilage pathogens 5. spoilage images 6. Measures to prevent spoilage of plant foods

3 Influences on the microflora of plants (I) The inside of intact and healthy plants is usually sterile. Only seeds and fruits can be contaminated during fertilization through the pollen tube inside the ovules. Plants can also be fecal contaminated by insects and birds as well as fertilization with unpasteurized sewage or compost from sewage treatment plants. The natural microflora includes all bacteria that can be found in the soil and thus on the surface of the plants. The germ count can be between 10 3 and 10 7 CFU / g.

4 Influences on the microflora of plants (II) Fresh vegetables are slightly acidic to neutral and enable bacteria to grow well. As a rule, only molds and yeasts can multiply in fruits. The epidermis of the plants, together with the cuticle and a more or less thick layer of wax, provide effective protection against the penetration of microorganisms. Uninjured parts of the plant can only be attacked directly through the enzymatic degradation of Erwinia species and some fungi. Many fungi also get into the interior of the tissue through stomata after initially growing only superficially

5 Influences on the microflora of plants (III) Numerous plants contain substances with a clearly bacteriostatic and fungistatic effect. They are therefore more durable. The following are to be mentioned: Benzoic acid in cranberries, blueberries, plums and other fruits Tannins in unripe fruits Essential oils in citrus fruits Mustard oils in radishes, onions and garlic Phytocins e.g. B. salicylic acid in grapes, strawberries, raspberries

6 Influences on the microflora of plants (IV) Phytoalexins are only formed after the plants have been infected by microorganisms (Phytohormone) can stimulate the formation of phytoalexins

7 Food spoilage Decay is the process of food deterioration, which means that food is no longer edible or even harmful to health. Decay is characterized by changes in appearance, consistency, smell and taste. The food law assessment is based on the degree of severity of these changes. The point in time at which a food is classified as spoiled and no longer marketable, however, also depends on regional attitudes and habits.

8 Causes of the spoilage of plant-based foods 1. Infestation by microorganisms Bacteria, yeast, mold 2. Biochemical changes in respiration, maturation, allelopathy 3. Physical changes Dehydration, withering, cold storage damage, freezing 4. Mechanical damage caused by transport

9 Biochemical changes Many types of fruit are dispatched when they are ready to be picked. The fruits have a hard consistency, a high starch content and usually a green color. Pre-climacteric (picking, harvesting, shipping or technical maturity) Biochemical processes lead to the formation of sugar from starch, so that the ripe fruits develop the typically sweet and sour aroma, combined with an increasingly softer consistency. Menopause (maturity for consumption or consumption) Beginning decomposition processes lead to a kind of self-dissolution. The pulp becomes floury, doughy, and an increasingly bland taste develops Post-climacteric (physiological ripeness)

10 Physical changes Dehydration, wilting of refrigerated products Due to the high water content of the perishable food, there is a vapor pressure gradient between the surface of the product and the room air. This means that fruits with a high water content, e.g. Apples, peppers etc. tend to give off water vapor until their ambient atmosphere has reached a level of humidity that is typical for them. This moisture is called equilibrium moisture. If this equilibrium humidity cannot be set or maintained, there will be shrinkage or loss of mass due to wilting.

11 Cold storage damage in fruit (chilling) Chilling are functional metabolic disorders that are irreparable and occur particularly with plant-based foods. By cooling below their chill point, the fruits lose their ability to ripen. Undercooled fruits "die" and can become a total loss. The transport and storage temperatures for fruit are well above their freezing point. The apple's heart tan is a clear sign of chilling damage

12 Microbial spoilage the sum of all adverse changes in food caused by the reproduction and metabolic activity of microorganisms. The effects of the microorganisms change the food both materially and structurally. The underlying degradation processes take place with flowing transitions in 2 phases:

13 1st phase Microorganisms use the low molecular weight substances freely available in food (dissolved in tissue and cell sap) as a source of energy, carbon and nitrogen. However, these substances are only partially broken down. Some of them are also converted into volatile, often strong-smelling products. Processes are often clearly recognizable by sensors as the beginning of microbial spoilage.

14 2nd phase As spoilage progresses, numerous enzymes are formed by the microorganisms, which then break down the main components of the food (higher molecular weight polysaccharides, proteins, lipids) into their lower molecular weight components. This is often associated with stronger structural changes in the food. The most important signs of spoilage are actually always the sensory (especially smell) recognizable changes.

15 Forms of microbial spoilage in fresh vegetable products Bacterial soft or wet rot caused by bacteria of the Erwinia genus occurs very rarely in fruit, practically only in pears, but almost every type of vegetable can be attacked, especially in a water vapor-saturated atmosphere in plastic bags

16 Corruption process Bacteria first feed on cell sap on the surface. Later they produce very active protopectinases, which dissolve the middle lamellae between the cells of the substrate. The tissue disintegrates in a mushy-greasy form with a bad smell of spoilage. After tissue disintegration, other types of bacteria such as Pseudomonas, Enterobacter and Lactobacillus species can multiply and further decompose the disintegrated cells.

17 Bacterial soft rot in leeks

18 Signs of putrefaction caused by yeasts and molds, usually only the fungal attack is visible, but before that there is often a massive increase in yeasts. Fungi use the alcohol formed by the yeasts from sugar as a carbon source only when this is consumed, enzymatic degradation takes place higher molecular substances caused by the fungi, combined with a directly visible tissue breakdown. Irrespective of the specific, sometimes very different pathogen fungi, in practice the deterioration patterns are differentiated according to their external appearance.

19 Significance of molds as food spoilers Colonization of various substrates possible Have a wide range of enzymes Numerous molds are mycotoxin producers Allergenic potential is a frequently underestimated problem characterized by i.d. Usually rapid growth in a wide temperature range (mesophilic and thermophilic molds), but growth below C is also possible. Molds are aerobic, but growth is still possible even with a low oxygen content

20 Genus Alternaria saprophytes widespread in the soil, on plant materials Field fungus from cereals, discoloration of flours, also in baked goods often in seeds (beans, peas, lentils, coffee beans, cocoa) decompose cellulose, pectin, lignin Growth up to 2 C possible mycotoxin Alternariol is suspected of being teratogenic, mutagenic and possibly carcinogenic. has allergenic potential

21 Genus Cladosporum very common food spoiler on cereals, vegetables (tomatoes!), In apple, grape and citrus juices a diverse material destroyer, also grows on plastics, corks of wine bottles can grow through it has a high lipolytic activity extremely psychrothrophic growth down to -10 C! often occurring indoors, in addition to other blackening fungi such as z. B. Alternaria, Curvularia or Ulocladium cause black discolouration on masonry and furnishings. Many allergic reactions to mold can be traced back to this genus, although Aspergillus and Alternaria produce the more potent allergens.

22 Aspergillus genus (watering can mold) occurs on fruits, vegetables, in flour, nuts, jam and bread, but also grows on cotton fabrics, jute on wood, paper and wallpaper. many species are producers of important mycotoxins e.g. B. aflatoxin, fumagillin, gliatoxin, ochratoxin, patulin have a very high allergenic potential blue-green colonies with sometimes felt-like mycelium

23 Aspergillus flavus predominantly found in warmer climates on grain and in nuts (peanuts, pistachios, Brazil nuts) Formation of aflatoxin B1, B2, G1 and G Growth at C and aw value of 0.78! A. fumigatus Occurrence in cereals and baked goods. Highest pathogenic potency of all Aspergillus species A. glaucus Further representatives of the Aspergillus genus. Decay of foods with a low water content, of foods with a high sugar content. Growth at -8 C to 43 C

24 Genus Penicillium (brush mold) numerous species, many of which are considered to spoil food, grow on fruit (especially citrus fruits, apples and peaches), bread, cheese, flour, jams and fruit juices.Some Penicillium species can contain mycotoxins such as Roquefortin C, patulin, glycopeptides or citrinine produce blue-green to olive-green colonies, e.g. T. with discoloration of the underside of the colony

25 further representatives of the genus Penicillium Penicillium expansum Storage mushroom on fruit, formation of citrinin and patulin Growth from -6 C to 35 C Penicillium italicum mainly found on citrus fruits Penicillium verrucosum more common storage and field fungus on cereals as well as on peanuts and vegetables forms ochratoxin A and Citrinine,

26 genera Mucor and Rhizopus worldwide occurrence are characterized by a very rapid growth have a wide range of enzymes important food spoilers, which can often be found on rotting fruits, in vegetables and on cereals optimum temperature is 37 C cause acute fungal infections (mucor mycoses) which are fatal, especially in immunocompromised people

27 Corruption images caused by mold in fresh fruit and vegetables Brown rot (Monilia, Sclerotinia rot) mainly occurring in pome and stone fruit The cause is Sclerotinia species (formerly known as Monilia). The infection already occurs on the tree through insect bites and minor injuries from environmental influences. diseased tissue parts are soft, initially light, later dark brown.

28 Green rot occurring mainly in pomaceous fruit and oranges caused by Penicillium (P.) species, P. expansum only affects ripe apples, i.e. it only occurs after long periods of storage, approx. 50% of the naturally occurring strains form the mycotoxin patulin fruits show an unpleasant mold taste even with a slight infestation. Transmission is possible from fruit to fruit or through packaging material, walls and ceilings. Beginning green rot on the apple

29 In citrus fruits, green rot is caused by P. italicum (blue mold) and P. digitatum (green mold). The type of mold that occurs depends on the storage temperature P. italicum can also assert itself at lower temperatures of 5-10 C. Most dreaded storage disease, is transmitted from fruit to fruit through contact. Citrus fruits are therefore often subjected to heat treatment after harvesting in order to kill any possible contamination with P. digitatum or P. italicum. Penicillium digitatum ghost hand

30 Gray rot caused by Botrytis cinerea in particular soft fruits and vegetables with a high water content such as strawberries, grapes, cabbage and lettuce are preferred colonized the mold usually grows very quickly and covers whole fruits or parts of plants within a few days. In addition to the ripe fruits, semi-ripe and green fruits can also be attacked on the plant. has a very high allergenic potential Botrytis grows at temperatures between 5 and 35 C with an optimum at C.

31 Brown or white rot (sclerotinia rot) caused by Sclerotinia sclerotiorum widespread storage disease in carrots, beets and celery infested parts of plants soften and are covered with white, cotton-like fungal mycelium; the mycelium excretes silvery, shiny, dew-like water droplets and is denser than in Rhizopus Mycelium can also grow in the wooden walls of warehouses and thus constantly re-infect the new stored goods.

32 Alternaria or black rot caused by various Alternaria species are particularly affected by tomatoes, peppers, carrots, celery and onions; the vegetables are coated with a dirty-gray, later black mycelium.

33 Rhizopus wet rot caused by various Rhizopus species characteristic white, woolly, wady mycelium with small black dots (sporangia) covers the mushy, wet rotten fruit and vegetables. Fungus is strongly pectinolytic, but mainly penetrates the tissue through injuries. is often spread by fruit flies

34 Measures to prevent microbial spoilage General precautionary measures during harvest Cold storage Delays the ripening process and the susceptibility to infection by lowering the temperature Storage under a controlled atmosphere Combination of cooling, increasing the CO 2 content and lowering the O 2 level Plant protection products and additives

35 Combating gray rot Researchers at the University of Freiburg discovered a natural repellant Bacteria of the genus Cupriavidus Breakdown of an oxalic acid derivative secreted by Botrytis cinera The acid dissolves the cell walls of the infected plant and the fungus can infect its host. The living area of ​​the Cupriavidus bacterium is the area around the plant roots.

36 Noble rot due to Botrytis cinera Grapes shrink like raisins and have a particularly high sugar content due to the loss of water. From these "noble rotten" berries, which are handpicked, the so-called "Trockenbeerenauslese" is produced in viticulture.