Advancing Cheese Production: Near-Infrared Spectroscopy in Quality Control

Abstract

Cheese is a fermented dairy product. It is distinguished by the various flavour, texture and aroma. To obtain a high-quality product with minimal costs, frequent monitoring of the cheese manufacture is required. Various sensory attributes or the properties such as the dry matter, total soluble solids, fat, crude protein, pH, rheological properties of the cheese could be analysed by the various descriptive, instrumental and computing method. One such method is the near- infrared optical technology. The study is conducted for understanding the role of near-infrared spectroscopy technology in the cheese manufacturing industry.

The recent advancement in the process analytical technique in near-infrared technology for the cheese product is reviewed herein. Near-infrared spectroscopy is an upcoming analytical technique which earns its popularity in the food industry due to its low maintenance or running cost. The advantage of the process analytical technology (PAT) in food industries is that it increases the process efficiency and final product quality by improving understanding and control of the process of manufacturing.

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Near-infrared spectroscopy (NIRS) is one of the important e-sensing technologies adopted in the PAT system. The application of the near infrared techniques is outlined or reviewed for the cheese product.

The monitoring of the cheese with the sensor technology is such a challenging but very imperative process. The use of this technology has many advantages, mainly to produce a high-quality product with minimal running and maintenance cost. Some advanced practices that are reviewed in this paper are for more future application of the near infrared technology for the food industry.

Introduction

Cheese is one of the milk-based fermented products. There is a wide variety of cheese which is distinguished by the flavour, texture and aroma. The food industry is more concerned about the safety and the quality of the food which are directly correlated to human health and social progress (Cen and He, 2007). Nowadays people are more concerned and just are eventually looking for high quality and trust marks on the food packs. Increased demand for high quality in food production requires a sophisticated analytical method for quality control (Porep, Kammerer and Carle, 2015). Therefore, the infrared analytical equipment has to potential to provide these benefits. Traditional analytical procedures are highly time-consuming, labour intensive, and very expensive. Therefore, the vibrational technique of process analytical technology such as Near-infrared spectroscopy provides a rapid and cost-effective alternative for producing a high-quality product (Porep, Kammerer and Carle, 2015).

In cheese, it is used to assess some properties such as the dry matter, fat, protein, pH and other rheological properties of processed cheese as penetration. There is different infrared spectroscopy method for rapid analysis of the cheese, mainly infrared absorption spectroscopy and then the Reflectance spectroscopy. The infrared absorption spectroscopy is mainly used for the liquid samples, thus the cheese products are blended and homogenized prior to analysis (Frank and Birth, 1982). While the latter does not require the sample preparation as above, it measures the intensity of the reflected light from the cheese surface (Frank and Birth, 1982). In recent years the evolution of the computer-assisted spectrophotometric equipment required for providing reflectance analysis to food material (Frank and Birth, 1982).

Nir Spectroscopy for Cheese Manufacturing

Fundamentals:

Near-infrared spectroscopy consists of a light source, beam splitter system, sample detector, optical detector and data analysing system (Prietoetal., 2017). Quartz-tungsten-halogen (QTH) lamps with the light emitting diodes (LED) are the most commonly used sources for NIR radiation. It is because of its low cost and high-intensity radiation in the NIR wavelength with its spectral output is continuous (Prietoetal., 2017). With the use of the LED system, the power requirement is much lower.

The NIR spectra interact with the sample and energy may be absorbed, reflected or transmitted. Various mode of measurements such as the transmittance, interacting, transflectance, diffuse transmittance and diffuse reflectance (Prietoetal., 2017). The NIR spectroscopy utilises either single channel (lead salt semiconductors such as lead sulphide 1100-2500nm, silicon detectors 400-1100nm) or multi-channel detectors (diode arrays or charged- coupled device) (Prietoetal., 2017).

Working principle:

The basic principle working of the near-infrared spectroscopy is that near-infrared light is directed onto a sample. The light is adjusted according to the composition of the sample. This modified light is thus detected. This technique is based on the molecular rotation and combinations vibrations (C-H, N-H, O-H AND S-H) (Bokobza, 1998).

The wavelength of the near infrared optical radiation is 780nm–2.5µm of the electromagnetic spectrum (Porep, Kammerer and Carle, 2015). According to Joseph and Gerald, the wavelength for reflectance spectra was over a range of 0.9500 to 1.8500µm for each natural cheese sample (Frank and Birth, 1982). In a review by the Frank and Birth, the cheese spectral analysis is done connecting a 14-monochromator scanning at 50 Å/s to a Neotec/Spectro computer. To a NeotecGQA sample holder, the cheese samples were placed. It holds the cheese sample firmly to the clear glass window with a spring pressure pad. The four lead sulphide detectors placed above the sample measures the reflected light. The drift of the equipment was reduced by scanning a halon standard for each 30 min (Frank and Birth, 1982). For the natural cheese, the data values were recorded at 10Å increment scanning. The reflectance data were analysed by computing correlations with the composition of the cheese (Frank and Birth, 1982). The data are thus collected and recorded on computers.

Process of cheese making

The product that is obtained from the coagulation of the milk protein (casein) and then separating the liquid (whey) and solid (curd) phases constituting the milk coagulum is known as cheese. The manufacturing process of the cheese is that the raw milk is first collected from the cow, where the initial temperature of it is 37 ℃. Then it is been taken to the cheese processing industry, the temperature of the milk is cooled to 4℃ while reception. The pre-treatment process is done for the cooled milk. The calcium which is precipitated phosphates re-dissolves, as well as the coagulating properties of the milk, are completely restored during the process of high-temperature short time pasteurization (72℃ for 15 sec), this helps in the killing of the pathogens (coliforms). Then the milk is cooled to the rennet temperature (32℃).

The separator separates the milk that is free from the bacteria and the other concentrate (spores and bacteria). For the inactivation of the spores (Clostridia microorganisms) present in the concentrate, the process of sterilization (plate heat exchangers) is done at 120℃ for one minute. After cooling (30℃) the concentrate is remixed with the clarified milk. The standardization of the fat is achieved either by in-line remixing after the separation or by mixing the whole milk and skim milk in the tank then pasteurization (72℃ for 15 seconds) is done. Then the milk is cooled to 32℃ needed for the starter bacteria to grow. The next process is to inoculation with the starter culture and is held for 30 minutes for ripening. To this calcium chloride, CO2, KNO3 and rennet are added at 32℃. Rennet is an enzyme that helps in forming curd by acting with the milk protein (Dairy Processing Handbook, 2018).

This is kept undisturbed for 30 minutes to form coagulum. Until it reaches a pH of 6.4 the curd can ferment. It is then cut into small pieces and heated to 38℃ for separating whey from the curd. Whey is then drained from the vat and the curd then forms a mat. The cheese is then salted (12 ℃) by sprinkling dry salt, they are then placed in cheese hoops and pressed into blocks to form cheese. They are cooled to 0℃ by keeping it in chillers. Finally, they are cut and packaged into blocks and transported to retail stores where the temperature is maintained at 4 ℃ (Milkfacts.info, 2018).

The high-risk part in terms of the food safety of cheese manufacture is at first the reception of the milk, the milk would contain microorganisms thus it should be pasteurized so that all the pathogens would be killed. The next part is that the sterilization part where the spores and the other bacteria are inactivated or kills. After the mixing of the whole milk and the skimmed milk, pasteurizing should be done to eliminate any cross-contamination. Finally, in the packaging, storage and transportation process these should be maintained at 0 ℃ and 4 ℃ respectively to protect the cheese from any microorganism and bacteria.

The procedure of cheese analysis in near-infrared spectroscopy:

The procedure used by Zink, Jeon and Harbers to find out the fat, protein and moisture content is that a few cheese samples from different manufacturers and various ages were purchased from the local supermarket. The composition in the cheese like the fat, protein and the moisture contents of the samples were done by Babcock fat test, Kjeldahl procedure and vacuum oven drying respectively A few cheese samples from different manufactures A few cheese samples from different manufacturers (Zink, Jeon and Harbers, 1989). These are the commonly used standard method by the dairy products industry. The samples are scanned with the Pacific Scientific 4250 Near Infrared ReflectanceSpectrophotometer. The procedure generally used for the study of the fat, protein and the moisture content are all the similar.

Chemometrics in the near-infrared spectroscopy

Chemometrics basically represents the application of the statistical and mathematical procedure to extract chemical and physical values. The most commonly used chemometrics methods are the multivariate calibration and multivariate classification. The objective of the multivariate calibration is to find quantitative relationships between two sets of measurement values. It is thus the spectra recorded by the near infrared spectroscopy and the results determined the conventional technology. The calibration method is used to predict the required parameters accurately from the cheese samples with the use of the rapid technique. The equation of the calibration depends on the number of samples used for quantitative and qualitative analysis.

According to Karoui and Debaerdemaeker, the combination of the NIR diffuse reflection with the multivariate chemometrics are used for the discrimination of the Emmental cheese of different origins. The linear discriminant analysis was conducted on the PCA score and thus it allowed classification of the investigated cheese because 100% correct classification was achieved for the Emmental cheese produced in the six different European places (Karoui and Debaerdemaeker 2007). The model with the 20 samples faced problems from over-fitting. More samples were required to substantiate those models. Thus, this allows more variability of the chemical properties and gradually developing mathematical models for the more good accuracy of the NIR technique (Karoui and Debaerdemaeker 2007).

The calibration is done in the near-infrared spectroscopy in the cheese manufacturing process (Zink, Jeon and Harbers, 1989).

Table 1: Calibration process (Zink, Jeon and Harbers, 1989)

Table 2: Statistical data for calibration set (Zink, Jeon and Harbers, 1989)

Reference

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