The primary purpose of the food industry is to provide consumers with products that are both safe and maintain most of their quality and organoleptic characteristics for a prolonged period. To achieve that, optimal food processing design is required to eliminate all pathogenic and spoilage microorganisms while retaining most of the food's quality attributes (Valdramidis et al., 2012). Based on the above, when deciding how to process a food product, such as fruit and vegetable purees, soups, milk dairy, and non-dairy products, and the list goes on, there is only one correct answer, which starts with “It depends”.
The decision to select the appropriate process for a specific food product depends on the following: safety, feasibility, quality, economics, sustainability, marketing, and consumers' perspective (Fig. 1). All the above factors will be described in detail in the following sections. Their importance in process decision-making is illustrated in Figure 1; as you can see, food safety is the most significant factor, non-negotiable (presented with bold boundaries compared to the others), and will be discussed in more depth in this scientific blog. The rest of the factors will be listed and discussed based on the order that appears in the figure, based on their importance in food safety and quality; however, their significance and their influence may be varied based on factors such as type of product, size of a food company, economics, marketing or other reasons.
Food Safety
Food safety is the most essential part of food processing. The safety of the final food product is non-negotiable and should not be compromised in any manufacturing decision. Food safety should be prioritized by taking any necessary regulatory or company internal actions such as good manufacturing practices, measuring, and record keeping of all critical parameters of the process, and finally by applying the appropriate food preservation actions, such as thermal or non-thermal processes, acidification, fermentation or drying, proper storage and transportation conditions (under refrigeration or freezing conditions), using the appropriate labeling such as "Ready to eat" or 'Thoroughly cook before eating" etc. Actions that ensure consumers' safety while maintaining the business brand "trustworthy".
Choosing the appropriate process based on food safety requires a good understanding of food microbiology, chemistry, and food engineering. More specifically, the first step in deciding the applied process requires understanding the microbiological challenges of that product under the used processing, transportation, and storage conditions. It depends on the product's characteristics, namely pH and water activity, and provides a good understanding of public health and spoilage microorganisms of concern that shall be controlled (Toledo et al., 2018; David et al., 2023). For example, it is well established in the literature that a food product with a pH higher than 4.6 and a water activity higher than 0.85 is prone to Clostridium botulinum (C. bot) growth. Based on the above, for a product like that, the appropriate thermal process, such as aseptic or canning if the product is stored and transported under ambient conditions or pasteurization (aiming to control C. bot thought) if the product is handled under refrigerated conditions) should be used to ensure that the finished product is safe for consumption (FDA, 2023).
On the other hand, high acid products (with a pH ≤ 4.6) that are designed to be processed and transported under ambient temperature, a milder thermal process is applied (either aseptic, canning, or hot-fill) to ensure the control of all pathogens of concern such as Listeria monocytogenes, Salmonella spp., Escherichia coli O157:H7, while also controlling more heat-resistance spoilages microorganisms such as molds, yeast, and enzymes (Toledo et al., 2018; David et al., 2023; FDA, 2023). For products with a very low pH (<3.8) that contain the appropriate acid (such as acetic (aka vinegar), a “cold fill” process may be applied if that has been established with a proper validation study (Breidt et al., 2013).
Another food category that has recently been paid attention to is low-moisture foods. In this category, the main preservation factor is the characteristic low water activity of these products, such as syrups, spreads, nuts, etc. These products may still require a thermal process or application of GMPs to ensure the control of Salmonella spp.
The other category is the “Ready to Eat” refrigerated products that require proper control of the pathogen of concern (based on the pH and water activity as discussed above) or any spoilage microorganism that can impact the product’s shelf-life. For refrigerated products, thermal (pasteurization) and non-thermal processes (such as High Pressure, Pulsed Electric Field, etc.) can be applied to achieve the required safety of the finished product.
The last category is the non-ready-to-eat products that require a cooking step by the consumers. For these products, proper microbial studies should have been conducted to ensure the microbial load of the products is not significant and verify the maximum shelf-life of the product under storage conditions. Furthermore, these products should have the appropriate label with the cooking instructions for the consumers.
Feasibility
Choosing the appropriate process to deliver the necessary safety to the food product depends on the feasibility of the method/equipment used. For example, achieving commercial sterility (shelf-stable product) of a tuna product requires an in-container canning process due to the solid phase of the product, making it impossible to use a continuous flow type of process such as aseptic. Based on the above, the product's attributes, including the product's type (liquid, solid, and multiphase (liquid product with particulates)) and viscosity, are critical for the feasibility of the process, packaging type, and equipment used (Toledo et al., 2018; David et al., 2023).
Furthermore, choosing the appropriate method, technology, and equipment is critical for process feasibility. An example is the process of highly viscous foods, such as fruit and vegetable purees, etc. These foods will require equipment that can deliver a more uniform treatment and bear food's viscosity, hence the pressure drop in the system. Therefore, these products are typically processed using scrape-surface heat exchangers or advanced heating technologies such as microwave or ohmic heating that enable the more uniform treatment of these foods (David et al., 2023).
Finally, another characteristic example is that non-thermal processes are not feasible to deliver shelf-stable commercial sterile products due to the limitations of these technologies to destroy spore-former microorganisms without adding heat (TetraPak, 2020).
Economics
Primarily the methods, technology, and equipment used depend on the equipment the processes that the business already owns and knows how to operate. For example, a company with a portfolio of retort-processed products will likely continue to use and follow the same processes and procedures.
On the other hand, for brand new process lines, the economics and the “size” of the food company play a crucial role in deciding the process and the type of equipment to be used to ensure a safe and quality final product. For example, for small/medium size companies that want to process a pasteurized juice product, alternative non-thermal technologies, such as high-pressure and pulse electric processes, can be considered a good option (TetraPak, 2020). These technologies preserve most of the product’s qualities compared to conventional methods. However, these technologies are more expensive than conventional thermal processes, and they have a small yield due to their batch or semi-batch technologies (high pressure) or limited volume capacity (pulse electric field). Based on that, companies that produce a significant amount of juice product per shift should consider the conventional thermal processes, using tubular or plate heat exchangers. Using the conventional thermal methods may result in slight degradation of the quality of the finished product (with the new (and more expensive) designs of heat exchangers, that is probably not true); however, it allows producing in continuous flow systems a significant amount of product per shift, while remaining economically less expensive compared to the non-thermal systems.
Quality
Food quality, namely nutrients, color, texture, and organoleptic characteristics, is essential for consumers' decisions and is one of the significant goals of food companies. Food products should be processed in such a way as to ensure food safety of the finished food while retaining most of the food quality attributes (Toledo et al., 2018; David et al., 2023).
As mentioned earlier in this blog, product characteristics (viscosity, liquid, solid, multiphase, etc.) are critical in choosing the proper process. Based on that, for low-viscosity products such as milk and dairy-based beverages, direct steam systems (steam injection or infusion) are ideal systems to process this type of product, resulting in a safe final product with high quality. For intermediate viscous foods, tubular heat exchangers are a good option. Recently improved designs of tubular heat exchangers have enabled us to improve heat transfer and reduce quality losses. High viscous food is typically processed in scraped surface heat exchanger, improving the uniformity of the process and minimizing quality losses. Moreover, newly developed advanced heating technologies, such as microwave and ohmic heating, have enabled food processors to produce high-quality viscous and multiphase foods. Advanced heating technologies provide rapid volumetric heating that ensures minimal process with a safe, high-quality finished product (Fig. 2) (Toledo et al., 2018; David et al., 2023).
Furthermore, for products processed with the retort, rotary retorts usually result in a better-quality finished product than other retort types due to enhanced heat transfer. Finally, non-thermal technologies such as high-pressure processes also result in high-quality finished products due to the volumetric uniformity of pressure application, but with the limitations discussed above (strictly pasteurized process, regulation in packaging, batch type of process, and expensive) (TetraPak, 2020).
Sustainability
Sustainability has become one of the hot topics and trends as the long-term goal in all industries and economies, including the food industry. A good definition of sustainability can be given from the following: Given constantly changing economic and environmental conditions, sustainable food processing is all about finding new ways of meeting present needs without compromising future viability. The food industry can be translated into three main categories: 1) minimize energy consumption and CO2 emissions, 2) minimize food waste, and 3) increase the use of more recyclable packaging materials.
From a food processing perspective, choosing sustainable food processing is a method of production using non-polluting methods, technologies, and systems that conserve non-renewable energy and natural resources, are economically efficient, are safe for workers, communities, and consumers, and do not compromise the needs of future generations. As a result, choosing newly advanced electric technologies is an excellent approach to sustainable food production. Electric-based food production technologies, such as MW and ohmic heating addition to the benefits described in food quality, can significantly reduce CO2 emissions and energy consumption (Grossmann et al., 2022), primarily if the electricity is generated through non-fossil-based sources. Another advantage of these technologies is that they are used mainly for shelf-stable products (David et al., 2023); hence, there is no environmental impact and energy requirements for refrigeration distribution and storage.
Marketing
In today’s digital world, with social media and the freely available information that consumers have instantly available, marketing can play an essential role in the decision-making of food production. For example, if consumers know the benefits (environmental, final food quality, etc.) may decide to buy a product that is produced by advanced electric heating technologies. A food company may decide on the food production method and technology based on how well it can be promoted to the consumers.
Another example of how marketing can influence processing decisions is with Califia Farms' unique bottle (Fig. 3). This brand has chosen a special shape bottle that has separated them from the rest of the competition and is probably more "attractive" or more "curious" for the consumers, with the associated benefits in marketing and sales. On the other hand, selecting that special shape bottle may have some cons on processing, namely due to its unique shape, it cannot be an aseptic packaging. Hence due to that limitation, the products in that type of bottle must be processed, distributed, and sold under refrigeration conditions.
Consumers’ Perspective
Finally, an example will be shared based on a personal conversation on how consumers' opinion finally plays the most crucial role in deciding if a product will go to the market and, in some cases, which process should be used. The paragraphs above describe the advantages of product quality (and overall food process sustainability) of advanced heating technologies such as microwave heating. A few years ago, a food company decided to test if they wanted to switch from their traditional retort canned cranberry sauce to an aseptic packaging, microwave-processed cranberry sauce. Both final products would be the same regarding food safety, shelf-stable, with a 12-18 months shelf life. The results comparing the two products were like what Figure 2 presents; the aseptic – microwave-processed cranberry sauce kept most of the raw material attributes, such as color, flavor, texture, and nutrients. As usual, before the final release (or decision), the consumer testing panel determines the final decisions. Consumers tasted both products and preferred the retort process product because they were used to the canned cranberry sauce more “burned” flavor and color. Hence, because the consumers were used to a specific type of product for cranberry sauce, the food company never changed its retort process. However, aseptically processed cranberry sauce was a better final product considering nutrients, color, texture, etc. The above-given example shows how essential consumers' perspectives on food business decisions and sometimes that can influence the processing.
Conclusions
As explained above, deciding which process to use is complicated and always starts with “It depends”. The used food process must result in a safe final product while retaining most of the food product’s quality attributes (flavor, color, texture, etc.) most economically and sustainably for the business and being preferable for the consumers in the very competitive food business market. So, deciding which process to use is complicated and depends on all factors described. However, it is essential to mention that food safety is the only factor that cannot be compromised. Hence, any process used must result in a safe final food product.
References
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Valdramidis, V. P., Taoukis, P. S., Stoforos, N. G., & Van Impe, J. F. M. (2012). ‘Modeling the Kinetics of Microbial and Quality Attributes of Fluid Food During Novel Thermal and Non-Thermal Processes,’ in P. J. Cullen, B. K., Tiwari, & V. P., Valdramidis (eds.), Novel Thermal and Non-Thermal Technologies for Fluid Foods, Elsevier Inc. USA.
WSU, 2023. Microwave Heating Fact Sheet. Accessed on June 9th, 2022. http://microwaveheating.wsu.edu/factsheet/index.html
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