High- and low-temperature drying and RAW foods: what are they and how do they differ?

High- and low-temperature drying and RAW foods: what are they and how do they differ?

You will surely have seen, on the shelves of specialized shops, foods labelled “RAW” or “100% RAW” - but have you ever wondered what exactly this means?

RAW foods are those whose processing phase has never exceeded the temperature of 42°C.

But why should temperatures be kept low during a food’s processing phases?

In general, when foods are subjected to heat treatments of any kind (cooking in water, “dry” cooking, drying, etc.), the nutrients naturally present in them undergo changes:

  • CARBOHYDRATES: transformations and rearrangements of nutrients in carbohydrates begin at temperatures above 100 C. Among these, one of the most significant is the Maillard reaction, which occurs between carbohydrates and proteins.
  • PROTEINS: proteins subjected to any type of heat treatment at high temperatures denature, i.e. they change their structure because the bonds that determine the shape of the molecule are broken. Very few proteins can withstand temperatures above 60-70°C for a prolonged period of time.
  • LIPIDS: above 100°C, unsaturated fatty acids begin to change.
  • VITAMINS: thiamine (vitamin B1), pantothenic acid (vitamin B5), folic acid (vitamin B9), ascorbic acid (vitamin C), and retinol (vitamin A) are all called “thermolabile” vitamins, which means that they lose their shape and biological function when subjected to high temperatures. The inactivation process for some vitamins already begins at 40-60°C, and the extent of the loss also depends on the type of treatment the food is subjected to.
  • MINERALS: it is difficult to estimate the extent of the loss of minerals during cooking as they are contained in food in a very variable form. However, most of the loss in mineral salts occurs when a food is cooked in water. Indeed, dry cooking, even at high temperatures, generally doesn’t considerably change the amount of minerals in a given food.

However, changes due to high temperatures are not always negative:

  • Denatured proteins are generally more digestible than those in raw products.
  • Some reactions involving carbohydrates give food peculiar but pleasant and refined sensory features (the browning of the bread crust, for example, is due to the Maillard reaction and consists in a rapid caramelization of sugars that occurs in the presence of proteins and at temperatures above 100°C).
  • Some substances considered “antinutrients“, i.e. toxic substances naturally present in food or substances that prevent the absorption of other nutrients, are inactivated.

Furthermore, high-temperature treatments kill the vast majority of microorganisms, including potentially pathogenic ones, that can contaminate food. Indeed, usually these bacteria proliferate at temperatures ranging from 5° to 60°C and die at higher temperatures. This means it is always advisable to cook foods well, especially those of animal origin such as meat, poultry, and fish, but also raw milk and fresh eggs.

At the same time, however, during high-temperature treatments there is a considerable loss and modification of nutrients and molecules:

  • Thermolabile vitamins and compounds with antioxidant action, such as carotenoids, suffer a decrease during cooking.
  • Unsaturated fatty acids oxidize at high temperatures (in the presence of oxygen) and cause rancidity.
  • Proteins and amino-acids undergo changes and denaturation that are not always positive.
  • Some high-temperature treatments cause the development of toxic substances.
It is difficult to generically quantify nutrient losses in any given, heat-processed food since the extent of the loss is closely linked to the cooking method to which it is subjected. In general, however, we can say that a product processed at high temperatures undergoes changes both on a nutritional and on sensory level (taste, smell and texture). Maintaining low processing temperatures therefore serves to prevent the nutrient content of the food from undergoing excessive alterations.

In light of this, when a product is labelled as raw, it means that it has probably kept most of its original nutritional and sensory characteristics intact. Those who follow a raw food diet (raw foodism or rawism) argue that, given that animals have evolved by eating raw, unprocessed, and wild foods, in order to make the most of the nutrients contained in food it is preferable to limit cooking and always use low temperatures. One can agree or disagree with this idea: it is true, for example, that raw fruits, vegetables, seeds, and nuts have a higher content of vitamins and antioxidant compounds than their cooked or toasted counterpart but it is equally true that the same cannot be said for other nutrients that are instead not available in raw food (in the sense that our body is not able to assimilate them) and are instead available after cooking.

Typical of raw food diets are treatments such as marinating and drying at low temperatures.

Drying is one of the oldest conservation techniques. This involves removing the liquid part from food, creating an inhospitable environment for bacteria and moulds and extending the storage period. It is particularly useful for all those products that have short storage times when fresh, such as fruit and vegetables but also meat and fish. The evaporation of the liquid part from food occurs after heating; with this method, the percentage of remaining water is around 10-15%, enough to considerably slow down the degradation process.

The ideal drying temperature for fruit is linked to the type in question as well as the drying method, which ranges from simple exposure to the sun and air up to more complex techniques. Drying times vary from a few hours to several days, and are strictly dependent on the temperature at which the process takes place: if a product is exposed to a high temperature, it will dry faster than a product dried at 42°C.

It is clear that removing water from fruit, at any temperature this occurs, causes alterations from the sensory point of view especially as regards texture and flavour. However, a product treated at low temperatures maintains both nutritional and sensory characteristics more similar to those of fresh fruit compared to products treated at high temperatures.

On Nuturally you can find an exclusive selection of Italian Nuts and Dried Fruit with no added sugar: dried at LOW TEMPERATURE, 100% RAW below 42°C, in order to maintain their nutritional and organoleptic properties unaltered and bring to you the taste and scent of the best fresh fruits. The dehydration of the products in the Italian Nuts and Dried Fruit category can take from 2 days up to a maximum of 1 week. These fruits are carefully cut by hand, with ceramic knives or mandoline, in order to avoid oxidization of the fresh product.  

Sources:

Data from Euro Company Analysis and suppliers’ technical sheets

Tom P. Coultate; La chimica degli alimenti; Zanichelli

Colli, P. Rossi, F. Marzatico; Viaggio negli alimenti; Calderini

https://www.fruttaebacche.it/blog/ce-differenza-fra-frutta-essiccata-frutta-disidratata/

https://www.repubblica.it/salute/alimentazione-e-fitness/2018/08/16/news/pazzi_per_il_cibo_crudo_benefici_e_rischi_del_raw_food-204104158/

https://cucina.corriere.it/notizie/cards/raw-food-regole-cucina-crudista/temperatura-non-oltre-42-gradi.shtml 

https://www.fondazioneveronesi.it/magazine/articoli/alimentazione/la-cottura-degli-alimenti-i-grassi

http://online.scuola.zanichelli.it/fanti-files/vitamine.pdf https://doc.studenti.it/vedi_tutto/index.php?h=dfc762d8&pag=1

http://www.salute.gov.it/portale/expo2015/contenutoExpo2015.jsp?id=116

http://online.scuola.zanichelli.it/barbonescienzeintegrate/files/2010/03/11_02.pdf http://foodsafety.asn.au/topic/temperature-danger-zone/

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