Related Experiment Videos
Chrysosporium species, potential spoilage organisms of chocolate
1Food Research Centre, Sheffield Hallam University, Sheffield, UK. j.l.kinderlerer@shu.ac.uk
Abstract:
Standard methods of analysing foods for the presence of moulds are inadequate for the detection of genera such as Chrysosporium which do not grow at the high water activities of most mycological media. The use of malt, yeast, 50% glucose agar (MY50G) in sealed containers as an enrichment medium allowed time for germination and growth of heat-stressed spores. Three Chrysosporium spp., C. xerophilum Pitt, C. inops (Carmichael) and C. farinicola (Burnside) Skou, were isolated from commercial chocolate bars with a water activity (aw) of approximately 0.28. Chrysosporium inops was isolated from commercial milk crumb and a new Chrysosporium sp. was isolated from Ghanaian cocoa beans. In chocolates made by coating MY50G agar (aw = 0.89) with chocolate (aw = 0.27) containing C. inops arthroconidia, two types of deterioration were seen after storage. The first was fat bloom due to recrystallization of the cocoa butter on the outer and inner chocolate surface. The second was growth of C. inops which occurred on the inside chocolate surface adjacent to the MY50G agar filling and on the outside surface after holding at 92% equilibrium relative humidity (erh) for 12 d. There was some evidence that C. inops could grow on the outside of chocolates held at 5.7% erh after 4 months' storage at 25 degrees C. The appearance of the white fungal growth was not unlike fat bloom to the naked eye but was clearly different with the electron microscope.
Insights
Standard food analysis methods fail to detect certain molds like Chrysosporium. A new enrichment method using malt, yeast, 50% glucose agar (MY50G) enabled mold detection in low-moisture foods, including chocolate.
Area of Science:
- Food Microbiology
- Mycology
- Food Science and Technology
Background:
- Conventional mycological media are unsuitable for detecting molds like Chrysosporium due to their inability to grow at high water activities.
- Standard food analysis methods are inadequate for identifying specific mold genera that do not thrive under typical laboratory conditions.
Purpose of the Study:
- To develop and validate an improved enrichment method for detecting heat-stressed mold spores, specifically Chrysosporium species, in low water activity foods.
- To investigate the occurrence of Chrysosporium in commercial food products like chocolate and cocoa beans.
- To assess the spoilage potential of Chrysosporium inops in chocolate under various storage conditions.
Main Methods:
- Utilized malt, yeast, 50% glucose agar (MY50G) in sealed containers as an enrichment medium to promote germination and growth of heat-stressed spores.
- Isolated Chrysosporium spp. from commercial chocolate bars, milk crumb, and Ghanaian cocoa beans.
- Conducted controlled storage experiments with chocolate samples inoculated with Chrysosporium inops to observe deterioration patterns.
Main Results:
- Successfully isolated three Chrysosporium spp. (C. xerophilum, C. inops, C. farinicola) from chocolate bars with a water activity (aw) of approximately 0.28.
- Identified Chrysosporium inops in milk crumb and a novel Chrysosporium sp. in Ghanaian cocoa beans.
- Observed two types of deterioration in inoculated chocolates: fat bloom and fungal growth of C. inops, which was distinguishable from fat bloom via electron microscopy.
Conclusions:
- The MY50G enrichment medium is effective for detecting heat-stressed Chrysosporium spores in low water activity foods, overcoming limitations of standard methods.
- Chrysosporium species are present in various food products, including chocolate and cocoa, posing a potential spoilage risk.
- Chrysosporium inops can grow on and within chocolate, leading to visible deterioration that can be mistaken for fat bloom.