In Europe, milk is defined as “the normal mammary secretion obtained from one or more milkings without either addition thereto or extraction therefrom” by the Council Regulation (EU) No 1308/2013 [1
]. People benefit from milk consumption, especially during the first years of life. Milk provides proteins of high biological value, lipids, vitamins and minerals (such as calcium) [2
]. Nevertheless, milk consumption is gradually decreasing in western countries [3
Nowadays the spread of alternative milk is growing (i.e., vegetables milk) commonly called “plant milk” or “non-dairy milk”. Consumption of “plant milk” is constantly increasing in North America as well as in Europe [4
The consumer choice of vegetable milk is related to health problems, such as lactose intolerance, milk protein allergy, phenylketonuria [5
]. An ever-larger portion of consumers, however, choose these beverages for other reasons such as religious motivations, the choice of diets that exclude animal foods or for taste. In addition, increasing urbanization has improved the demand of functional and healthy beverages [7
All plant milks are obtained by the same procedure. Figure 1
shows the production flow-chart. First the raw material is crushed, then the obtained flour is mixed with water. After being filtered, the vegetable milk is ready. Industrial productions can also be continued with other ingredient additions or heat treatments [8
]. Oil, flavorings, sugar, and stabilizer are the most common ingredients added. Homogenization and ultra-high temperature (UHT) treatments (rarely pasteurization) are performed to improve suspension quality and microbial stability [9
Soybean milk is the most ancient and widespread non-dairy milk. However, preparation originating from other plants belongs to many world cultures (atole from Mexico, horchata from Spain, bushera from Uganda, etc.) [9
]. According to a recent study [8
], there is no shared definition and classification of these plant milks.
A general classification in categories has been proposed:
Cereal based: Oat milk, rice milk, corn milk, spelt milk, millet milk;
Legume based: Soy milk, peanut milk, lupin milk, cowpea milk;
Nut based: Almond milk, coconut milk, hazelnut milk, pistachio milk, walnut milk;
Seed based: Sesame milk, flax milk, hemp milk, sunflower milk;
Pseudo-cereal based: Quinoa milk, teff milk, amaranth milk, buckwheat milk.
Plant milks have a lower nutritional value than milk, they lack important proteins, vitamins and minerals. Plant milks, however, are beverages that have beneficial health characteristics [10
]. For example, in vegetable milks, there are phytosterols despite cholesterol being widely present in milk. They contribute to fiber intake and are often reinforced with vitamins and minerals. Plant milks are recommended for milk allergy sufferers (no lactose, no milk protein) and some of these are also gluten-free and nut-free [11
An important characteristic is the presence of phytochemicals, substances known to have positive effects on health. Oat milk, for example, contains b-Glucan, with a hypocholesterolemic effect by reducing total and low-density lipoprotein (LDL) cholesterol. Sesame milk instead contains lignans which have antioxidant, anticarcinogenic and anti-tumor activity [8
There is no specific regulation of plant milks, so in the same category they can have a great difference in composition values. Therefore, to ensure quality and safety of these products, the detection of suitable molecular markers is required.
Biogenic amines are ubiquitous compounds and derive from amino acids decarboxylation. This reaction is caused by endogenous enzymes or microorganisms, therefore biogenic amines can be endogenous or exogenous. Endogenous biogenic amines are part of many cellular functions, with very different effects. Great attention is given to the study of biogenic amines content in food [12
]. They are present in all food, especially in the protein ones or in fermented products, like fish, meat, wine and dairy products [13
]. Low levels of biogenic amines are a natural characteristic of some fermented food (cheese, sausage, etc.) and contribute to define their aroma [17
]. Excessive presence of biogenic amines can cause headaches, tachycardia and nausea but also, in extreme cases, cerebral hemorrhage, anaphylactic shock and death. In addition, some biogenic amines show a vasoconstrictive or vasodilator effect. The most dangerous biogenic amines for human health are histamine and tyramine. Phenylethilamine, serotonin, putrescine and cadaverine can have toxic effects enhancers by hindering the body’s enzymatic detoxification mechanisms. Starting from recent studies, also alcohol intake seems to increase the amines absorption rate [18
]. Histamine and tyramine are responsible respectively for sgombroid syndrome and the cheese crisis [19
]. A scientific opinion from the European Food Safety Authority has established the biogenic amines safe intake dose (per meal) is 50 mg of histamine and 600 mg of tyramine [20
Several authors have proposed biogenic amines as food quality and safety indicators, also in beverages. Poveda investigated the difference in the amino acid profile and the biogenic amines content in craft beers from the Spanish market. The results showed a relationship with raw materials and brewery [21
]. A recent study evaluated the profile of biogenic amines in fruit juices and fruit nectars, and then classified them according to the fruit of origin [22
]. However, many studies have focused on wine, in which biogenic amines can represent a great problem for consumers. Higher biogenic amines content have been found in red wines than the white ones, especially wines obtained by malolactic fermentation [23
]. Moreover, biogenic amines were also investigated in cow’s milk and soy drinks [25
Nowadays, the high-performance liquid chromatography (HPLC)-based method is considered the “golden standard” method for biogenic amines determination [27
]. This method has high sensitivity and allows the simultaneous quantitation of several biogenic amines in food. The European Union has defined a HPLC method, coupled to a pre-column derivatization, for histamine routine control in fish [28
The aim of this study was to characterize the main cereal and pseudo-cereal based milks found on the market by evaluating the profile of 8 biogenic amines (histamine, serotonin, spermine, spermidine, putrescine, β-phenylethylamine, cadaverine, tyramine) by a reverse phase liquid chromatography method coupled with a spectrofluorimetric detector (RP-HPLC-FD) and pre-column derivatization. Starting from the results, it was possible to evaluate the identification of biogenic amines to use as safety and quality markers in plant milk. Starting from literature research, few works describing the presence of biogenic amines in alternative milks, especially in soy milk [26
], were found and not one in cereal milks. So, to the best of our knowledge, this seems to be the first study that investigates the content of biogenic amines in cereal and pseudo-cereal milk.
This study evaluates the biogenic amines content of six different classes of cereal and pseudo-cereal milks, chosen as the bestselling dairy alternative (excluding soy milk). This is the first investigation on the presence of eight biogenic amines in cereal and pseudo cereal milks.
The results show that the beverages are not biogenic amines free, as expected, due to the water extraction step in the production process [9
Histamine, cadaverine, tyramine, spermidine and spermine were found in the samples.
The total biogenic amines content ranged from a minimum of 1.92 mg/L, to a maximum of 9.27 mg/L and the BAI was under 10 for all products analyzed. The main biogenic amine in the samples was histamine. Biogenic amines are usually considered as quality and safety markers. Cereal and pseudo-cereal milk samples shown low content in biogenic amines, therefore they can be considered safe and quality products.
Moreover, statistical analysis has shown that barley milk has a different BAs profile compared to the other classes.
Further studies need to be conducted by expanding data-set in other classes and variables. Future experiments can be conducted to monitor the evolution of the BAs profile during shelf life, as well as to evaluate the biogenic amines in products derived from these milks (dairy free yogurt, dairy free cheese, etc.).