Traditionally, the production of pasta is said to originate in China, but pasta was known many centuries before in the Mediterranean area. Etruscan people knew the technique of preparing noodles or lasagne, while the description of this food was found in many documents from the Greco-Roman age [41
]. Over time, pasta became increasingly important in the South of Italy, thanks to the optimal climatic conditions for the durum wheat cultivation and for pasta drying. With the globalization of the agro-industrial culture, including the change of dietary habits, pasta became popular worldwide. Today, pasta represents a primary component of the diet in many countries [42
The conventional process for pasta production does not include a fermentation step. Pasta is traditionally produced by a rapid extrusion of a durum wheat semolina dough through dies, followed by a drying stage in strictly controlled conditions (dried pasta).
With the aim of enhancing the nutritional and functional properties of pasta, as well as enriching the commercial offer with products with new sensorial profiles, different recipes including sourdough-fermented ingredients have been recently proposed.
2.1. Nutritional Aspects
The use of refined wheat flour, although having high technological properties and stability, leads to the obtainment of food containing less of the beneficial compounds mostly present in germ and bran, like dietary fibers, vitamins, and polyphenols. Today, thanks to the increased consumers’ attention towards the nutritional properties of foods, the demand for food products with a well-balanced nutritional composition is increasing. For this reason, the use of sourdough for pasta fortification has been investigated in several ways, including the fortification in vitamin B, riboflavin, and the reduction of starch digestibility and GI.
In cereals, a large portion of vitamins is located in the germ and aleurone layer, which are removed during milling. In particular, B-vitamins are an essential component of human diets, as they support growth, erythrocyte formation, and the energy-producing metabolism. Riboflavin is a B-group vitamin, mostly present in the aleurone layer of wheat, it is stable to high temperature, high oxygen and acid content but unstable to alkali and light exposure [43
]. Riboflavin deficiency is found in 6–15% of the worldwide population and persists in both developing and industrialized countries. Many microorganisms, including LAB, have been studied for their capability to produce riboflavin. The use of riboflavin producing LAB has emerged as a tool to produce fermented and fortified foods at the same time [45
]. Recently, aiming at vitamin fortification of wheat flour to be used in pasta making, LAB strains were selected based on roseoflavin-resistance assay, riboflavin synthesis capability, and stability of riboflavin-overproducing phenotype [42
]. Their use was proposed as an alternative way to increase riboflavin content in cereal-derived products, instead of the addition of the chemical synthesized one. In particular, riboflavin-overproducing Lactobacillus plantarum
UNIFG1 and UNIFG2, isolated from sourdough, were used as starters for a pre-fermentation step of semolina and finely ground semolina (re-milled) [42
]. The latter was the most suitable substrate for riboflavin fortification by LAB, probably because the re-milling process provides damaged starch, promoting LAB growth. Riboflavin content was monitored during all the steps of the pasta production process, including mixing, extrusion, and drying. The final concentration determined after cooking was ca. 2.48 μg/g. Taking into account 100 g of serving portion, fortified pasta can significantly contribute to riboflavin intake, considering values of 19.2% of the Reference Daily Intake (RDI) for men, and 22.7% of the RDI for women [46
Low GI diets have been shown to protect against type II diabetes, cardiovascular disease, obesity, metabolic syndrome, and some types of cancer [47
]. Since human diet is based on staple starch rich foods—such as rice, bread, and pasta—many attempts have been made to reduce starch digestibility, gelatinization, and hydrolysis rate or increase the undigestible starch fraction in foods, especially concerning the prevention of the above conditions in industrialized countries. Overall, pasta GI is lower than that of bread [48
], and commonly ranges from 40 to 60 [48
]. Nonetheless, common pasta portion sizes (i.e., 80–100 g) often provide relevant amount of carbohydrates in the diet [49
], and GI reduction is considered one of the main objectives of the scientific and industrial research on pasta [50
Sourdough fermentation strongly affects starch digestibility and GI of leavened baked goods [3
], thus it is potentially applicable also in pasta making. The production of organic acids during sourdough fermentation has many positive effects on starch digestibility: lactic acid is responsible for low starch digestion, while acetic and propionic acids for the prolonged gastric emptying rate.
In particular, it was hypothesized that lactic acid promotes the interaction between starch and gluten, thus limiting starch bioavailability [53
]. This phenomenon is not solely due to the pH drop, but is correlated with the specific organic acid.
A recent study evaluated the starch digestibility in fresh pasta manufactured with semolina-based liquid sourdough fermented by Saccharomyces cerevisiae
PCC1140 and Lactobacillus alimentarius
PCC859. Sourdough fermentation did not affect the total starch content but induced several molecular changes. Compared to an unfermented control, sourdough led to the decrease of the slowly digestible fraction (43.0% vs. 49.8%) and to the increase of the not-digestible (40.2% vs. 34.5%) and retrograded starch fractions [54
2.2. The Celiac Issue and Gluten Reduction
Gliadins and glutenins are the protein fractions of wheat responsible for the formation of gluten during the mixing of flour with water. Products made using wheat or other cereals, in which homologous proteins are found, like rye and barley, are associated with gluten related disorders [55
]. These disorders (celiac disease, wheat allergy, and non-celiac gluten sensitivity) having an estimated global prevalence around 5%, could show similar clinical manifestations and are due to gluten assumption. Celiac disease and wheat allergy could be diagnosed based on a combination of the patient’s clinical history and specific tests, while non-celiac gluten sensitivity is still considered a diagnosis of exclusion, in the absence of clear-cut diagnostic criteria [55
]. Gluten sensitivity symptoms disappear in people that follow a gluten free diet. Nevertheless, the threshold of gluten intake related to the adverse reaction in subjects affected by gluten sensitivity is still debated and it has not yet been precisely established [56
]. People suffering from gluten sensitivity are commonly affected by irritable bowel syndrome (IBS), an intestinal disorder that causes abdominal pain, bloating, diarrhea, constipation, and gut microbiota unbalance [2
]. Besides gluten, IBS is also related to the intake of other nutrients or ANFs such as lipopolysaccharides, amylase/trypsin inhibitors, wheat germ agglutinins (WGA), and fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs) [57
To date, the only treatment to avoid complications is a gluten-free diet. Europe and United States law set the limit to define gluten free products to 20 ppm [58
]. This limit is also applied to ingredients and food where a gluten-containing grain or flour is used, but have been processed to remove gluten.
Sourdough biotechnology was used to reduce gluten content of wheat flour under the limit of 20 ppm to produce gluten free pasta [60
]. The process included the development of a semi-liquid dough having dough yield (DY, dough weight × 100/flour weight) of 220, which was fermented for 24 h at 37 °C with four selected LAB (Lactobacillus alimentarius
15M, Lactobacillus brevis
14G, Lactobacillus sanfranciscensis
7A, and Lactobacillus hilgardii
51B) previously isolated from sourdoughs [16
]. These LAB were selected based on their ability to hydrolyze gliadin fractions and various proline-rich oligopeptides, including the 33-mer epitope, considered as the key-factor in determining gluten-related disorders [61
]. After fermentation, the sourdough was freeze-dried and milled to be used as fermented ingredient in the final recipe of pasta. A 3:7 ratio of sourdough flour and buckwheat (Fagopyrum esculentum
) flour, respectively, was used. Different tests were performed to define the degree of protein hydrolysis, focusing on gliadins degradation. In particular, a specific sandwich ELISA (Enzyme-Linked Immunosorbent Assay) based on the use of the R5 antibody, commonly used to identify immunoreactive proteins and peptides able to induce toxic responses in celiac patients, showed a gluten concentration five-folds lower in experimental fermented pasta compared to the unfermented control [60
The sensory analysis revealed that the experimental pasta was less sticky and firm than pasta made without fermentation, without any other significant difference.
In a follow up study, a process to manufacture pasta with a higher amount (50%) of wheat flour, rendered gluten-free through LAB fermentation, was developed [50
]. The bioprocess consisted of fermentation of wheat flour by sourdough lactic acid bacteria (Lactobacillus sanfranciscensis
7A, LS3, LS10, LS19, LS23, LS38, and LS47, Lactobacillus alimentarius
15M, Lactobacillus brevis
14G, and Lactobacillus hilgardii
51B) previously selected based on their ability to hydrolyze Pro-rich peptides [50
] in the presence of fungal proteases (from Aspergillus oryzae
and Aspergillus niger
). Wheat flour bioprocessing was carried out at 30 °C for 48 h. For pasta making, 50% of the above freeze-dried sourdough (DY of 500) and 50% of pre-gelatinized rice flour, calculated on the total amount of flour, were used. Fermentation led to an increase of total FAA and peptides in the water-/salt-soluble fraction, deriving from the gliadin and glutenin proteolysis. Particularly, the amount of amino acids was 15-folds higher than that found in the unfermented dough (0.987 ± 0.043 vs.15.212 ± 0.125 g/kg). The gluten content of fermented dough was lower than 10 ppm. The nutritional indexes of rendered gluten free wheat pasta were similar to those of commercial durum wheat pasta. The in vitro protein digestibility and the protein efficiency ratio (PER) were higher in the experimental sample. An acceptable structure of pasta made using sourdough was kept thanks to pre-gelatinized rice flour [62
]. Moreover, fermentation led to the decrease of the starch hydrolysis rate and hydrolysis index (HI) to 58.8% [50
]. The authors concluded that the use of wheat flour rendered gluten-free in pasta could be considered a good alternative to other gluten-free ingredients (rice or maize flours) usually employed in gluten-free formulations.
In a recent study, pasta with a reduced gluten content was produced using fermented semolina [56
]. Gluten hydrolysis was carried out by sourdough fermentation using a pool of selected lactobacilli and fungal proteases [50
]. Pasta made using the treated flour (containing 50% of the native gluten) had lower amount of Ca++
and did not show significant differences in FODMAPs content compared to the control, made with native wheat flour. Experimental pasta was tested in a randomized crossover-controlled trial on 20 IBS patients showing the positive effect of reduced gluten pasta after 2 weeks of daily consumption [56
2.3. Textural and Cooking Properties and Sensory Profile
The main technological parameters of pasta made with unconventional and fermented ingredients are generally determined after cooking, since this process causes relevant changes in physicochemical characteristics of the product.
Optimal cooking time (OCT, defined as the time needed for the disappearance of the white core) and cooking loss (corresponding to the amount of solid residues in cooking water), are considered as quality parameters for pasta. Shorter OCT and lower cooking loss for pasta made with fermented flour compared to the unfermented control were observed [54
]. In the above study, a correlation between the use of sourdough and firmness increase was reported, thus hypothesizing a positive effect of organic acids in the interaction between starch and gluten, which contributed to obtaining a firmer network [54
Nevertheless, several studies highlight the strict dependence of the textural properties from the amount of fermented flour included in the recipe as well as the fermentation parameters (e.g., fermentation time, degree of proteolysis). For example, when semolina was fermented aiming at decreasing gluten, the technological quality of the pasta became inferior, if compared to the unfermented control [50
]. In particular, cooking loss increased and firmness decreased, due to the extensive proteolysis occurring during LAB fermentation, which weakened the gluten network.
The structure of pasta obtained with wheat flour rendered gluten-free by fermentation in combination with rice flour [61
] was analyzed through epifluorescence/fluorescence microscopy. The analysis of the microstructure revealed the extensive protein degradation of the fermented wheat flour, and the presence of few and disorganized protein spots deriving exclusively from rice flour. The protein structure of pasta containing fermented wheat flour presented inhomogeneous aggregates, similarly to those commonly observed in commercial gluten free pasta (made with natural gluten-free ingredients), but completely different from the homogeneous reticular structure observed for conventional durum wheat pasta. The starch structure appeared similar in all samples analyzed. As expected, in conventional pasta the strong gluten network avoided starch swelling and deformation during cooking, phenomenon characterizing commercial and rendered gluten free pasta. In these cases, amylose leaked out of the granules. As the consequence of the microstructure organization, textural properties of pasta made with rendered gluten free flour were similar to those of commercial gluten free pasta (made with natural gluten free ingredients, mainly rice and maize flours). Nevertheless, hardness, gumminess, and chewiness, determined by instrumental texture profile analysis, were significantly higher in the experimental gluten free pasta compared to the commercial counterpart.
Overall, sensory analysis showed that pasta made with fermented flour significantly differed from conventional products. Clearly, many sensory properties were associated to the textural features. Several studies demonstrated that acidic smell and flavor derived from LAB fermentation were markedly attenuated by cooking, thanks to the high temperature and the solubilization of hydrophilic small compounds in water. Nevertheless, also in this case different results were observed on the basis of the amount of fermented flour included in the recipe and the related fermentation parameters.
When 30% of native wheat flour was substituted with freeze dried wheat flour previously fermented by a selected pool of LAB, lower scores for stickiness and firmness perception were found in comparison to the control, a pasta formulation made with the same recipe but including only unfermented ingredients. Overall, odor and flavor did not significantly differ between the two products, and the experimental pasta was positively judged [50
No significant differences were found for perceived stickiness, presence of flaws and chewiness between a commercial gluten-free pasta and an experimental pasta obtained using wheat flour rendered gluten-free by fermentation [61
], although an unusual taste characterized experimental pasta, probably due to the acidity derived from the fermented wheat flour component. However, the overall acceptance was not affected, even though the experimental pasta including fermented wheat flour presented the lowest lightness.
Besides the potential application in gluten degradation, sourdough fermentation was used to improve the quality of natural gluten-free ingredients. Among these, sorghum is considered an excellent source of proteins and antioxidant compounds [63
]; it is also characterized by a lower amount of starch, compared to other cereals, which is of interest for diabetic or obese people [64
]. A dried sorghum sourdough (DY of 300) was employed as pasta ingredient [65
]. In particular, the fermented sorghum was mixed with parboiled brown rice and pre-gelatinized rice flour at 15% w/w in the final recipe. The addition improved pasta cooking quality compared to the control containing unfermented sorghum, with lower firmness and cooking losses, and higher water absorption [66
]. The low cooking loss reflected a suitable protein linkage, positively contributing to a stable network in the final product [65
lists, not exhaustively, the characteristics of the experimental pasta made using the fermented cereals flour described before.