In addition to threatening public health, food spoilage should be identified as soon as possible, the underlying cause should be revealed, and treatment should be initiated as soon as possible due to increased hospital costs, incapacity to work, and economic problems as a result of the consumption of foods that couldn’t be detected at the time that they are spoiled (Odeyemi et al. 2020; Pellissery et al. 2020). Classical microbiological analyzes take longer to complete, and ddPCR analyzes provide both fast and quantitatively reliable results. For this reason, the usability of ddPCR in the detection of food spoilage was investigated, the amount of histamine and putrescine biogenic amine, which is a spoilage product, was determined by ddPCR, and the parallelism of the increase in this product with the spoilage was investigated in this thesis study. There are several microorganisms that produce putrescine and histamine, but it is impossible to study each one separately. In this study, the quantity of hdc and agdi genes responsible for the production of these biogenic amines was therefore determined. This number of hdc and agdi genes was compared with the results of the classic microbiological analysis, and it was investigated whether this method could be used to determine food spoilage.
Smart packaging, one of the new packaging systems, allows monitoring of the condition of the food as well as providing information about different changes during transportation and storage (Kalpana et al. 2019). Time-temperature and freshness indicators are the smart packaging systems used for this purpose (Fang et al. 2017). In this study, with the help of these indicators, it was evaluated whether two of the sub-members of the smart packaging system could be used in the detection of food spoilage. In the freshness labels, the results related to the pH change were observed in the control groups, it was determined that the color of the label changed as the pH increase occurred, and the indicators used were observed to be successful. Successful results have been obtained in many studies in which the freshness of chicken meats is monitored with pH-sensitive indicators (Riahi et al. 2019; Lee et al. 2019; Wu et al. 2021). In this study, deviations were observed in freshness indicators in MAP packaged product groups. When the studies in this area are reviewed, it has been observed that the freshness indicator, which is sensitive to other spoilage products such as sulphured compounds, is generally used in MAP products (Smolander et al. 2002; Opara et al. 2022). When the performance of the freshness indicators was evaluated, it was interpreted that the factors other than the product in the package (such as the additional gas in the package) should be further developed for the use of pH-sensitive freshness indicators in the MAP system, since the indicators show a color (pH) change that is not due to spoilage.
The time-temperature indicators used in this study showed that they can be used effectively in the smart packaging system by not changing color as long as there is no deviation in temperatures in both MAP and control groups. Studies in the field of TTI also support that this product can be used effectively for the monitoring of food spoilage (Mataragas et al. 2019; Vaikousi et al. 2009; Gao et al. 2020). Results will be much more effective when the time-temperature and freshness indicators are combined with other smart and active packaging systems.
It has been confirmed by previous studies that the amount of biogenic amines, which is one of the food spoilage products, increases as a result of the spoilage of chicken meats (Wojnowski et al. 2019; El-Nour et al. 2017). Rokka et al. reported that there was no significant change in the amount of putrescine below + 6.1°C, on the other hand, an increase in the amount of putrescine was reported after 7 days when it was above this temperature (Rokka et al. 2004). In another study, it was observed that the amount of putrescine and histamine in chicken meat stored at 4°C began to increase significantly on the 15th day (Silva and Glória 2002). Gallas et al. observed that there was an increase in putrescine on the 9th day, and a slight increase in histamine in their study on MAP packaged chicken meat, while Balamatsia et al. pointed out that the amount of putrescine detected by the HPLC method increased from the 5th day (Gallas et al. 2010; Balamatsia et al. 2006). In another study, it was disclosed that putrescine began to increase from the 3rd day and histamine began to increase from the 7th day in chicken meat that is in cold storage (Baston and Barna 2010). Baston et al. stated that putrescine in chicken meats in cold storage increased after the 7th day and histamine increased after the 20th day (Baston et al. 2008). In this study, we noticed that the number of bacteria producing histamine and putrescine gene started to increase on the 3rd day in both MAP and control groups. This is an indication of the onset of spoilage from the 3rd day. However, since the studies are based on the direct detection of the presence of biogenic amines, the presence of spoilage was detected a couple of days later. There is a serious risk of a public health threat since the product will not be detected to be spoiled during this period and will be consumed.
Many bacteria cause the production of histamine and putrescine, which are closely related to spoilage (Moniente et al. 2021; EFSA 2011; Chaidoutis et al. 2019). Since it is not possible to analyze all these bacteria separately, both economically and practically, the numbers of genes responsible for the production of these biogenic amines were determined and this amount was compared with the classical microbiological analysis findings and it was investigated whether or not this method could be used in food spoilage detection. Previous studies have shown that PCR or Real-time PCR methods have been generally used in the detection of these genes (Moniente et al. 2021; Nurilmala et al. 2020).
In our literature review, we could not find any study that the ddPCR method was used for the detection of spoilage, therefore, unlike other molecular methods, we aimed to use the ddPCR method in this study. Studies in the field of ddPCR have proven the reliability of this method. As a result of their study, Pinheiro et al. found ddPCR to be successful and made successful measurements even in samples with less than 5% DNA density (Pinheiro et al. 2012). Contrary to qPCR, it is not sensitive to inhibition of amplification in DNA extractions and can give accurate results even in very small sample amounts (Morisset et al. 2013). Being able to analyze even a single copy is a reason for preference, especially in areas of vital importance such as cancer studies (Galbiati et al. 2019). In the food industry, it is used in many areas such as the determination of the different meat types added for fraudulent purposes (Ren et al. 2017; Naaum et al. 2018), pathogen detection (Cremonesi et al. 2016; Pan et al. 2020) and GMO analysis (Košir et al. 2019). However, since no study was found using ddPCR to detect food spoilage, the results of this study were expected to serve as a roadmap for future research in this field.
Until 7 log10 cfu/g microorganisms are detected, there may be no odor or taste change in food, or the consumer may not accept that the food is spoiled for thriftiness and consume it, which may cause food poisoning (Sperber 2009). This process is affected by many factors such as the structure of the food, its type and storage conditions. Hinton et al, in their study, observed that there was an increase in spoilage bacteria on the 7th day in chicken meat stored in cold storage, and a significant increase in the number of Pseudomonas spp. on the 7th day (Hinton et al. 2004). Also, the psychotropic nature of Pseudomonas spp. allows it to be used as a spoilage indicator in foods stored at low temperatures (Martínez et al. 2011). In chicken meats, the development of Pseudomonas spp. is rapid and these bacteria can be used as a freshness indicator (Bruckner et al. 2013). Studies show that lactic acid bacteria and Enterobacteriaceae are also the dominant flora, especially in MAP chicken meat, and cause food spoilage (Tsafrakidou et al. 2021; Lauritsen et al. 2019). Our study showed parallelism in with the high levels of biogenic amine producing genes of those bacteria in spoiled chicken meats.
Jaafresh et al, in their study based on the detection of spoilage in MAP packaged chicken meat, considered the group between 4–9 days as semi-deteriorated while considering the group after the 10th day as spoiled and determined 9 days as the storage period (Jaafreh et al. 2018). In our study, it was accepted that there was an increase, especially in the psychrophilic group from the 9th day and although the storage times of the products in MAP packaging were longer, the control group deteriorated by the 9th day.
As microbial deterioration begins, pH changes also begin and this is reflected in the data. In MAP and air-packed chicken meats, pH was measured between 5.8 and 6.4 as a result of spoilage, and no differences were observed according to gas ratios (Rossaint et al. 2015). Herbert et al. also stated that gas differences and time do not affect pH and the pH is generally between 5.7–6.2 in chicken meats (Herbert et al. 2013). Bruckner et al. found that the pH increased from 6.02 to 6.23 in chicken meats stored at 4°C (Bruckner et al. 2013). In this study, there was an increase in pH values for each group, similar to other studies. In addition, the pH changes of MAP, which has lower microbiological values, were relatively less than the control groups.