2.2.9. Sensory Analysis

The sensory evaluation of the biscuits took place in the Laboratory for Sensory Analysis from the authors' faculty, under normal daylight conditions. All samples were evaluated for acceptability using a nine-point hedonic scale. A total number of 52 evaluators (40 females and 12 males) between 19–52 years old participated at the study. The evaluators were students and staff members from the Faculty of Food Science and Technology, selected on basis of their interest, availability and regular consumption of biscuits (at least once per week). Samples were coded anonymously with a three digit code and presented on plastic odour-free plates, in random order. Two replications of each sample were evaluated by each participant. Plain mineral water was provided to clean the palate between samples. Five sensory characteristics were rated on the nine-point hedonic scale: "appearance" (1 = extremely irregular surface, 9 = extremely regular surface), "hardness" and "crispiness" (1 = extremely weak, 9 = extremely strong), "chewiness" (1 = extremely difficult to chew, 9 = extremely easy to chew) and finally, "taste and aroma" (1 = no flaxseed taste and aroma, 9 = extremely strong flaxseed taste and aroma). The attributes of hardness were explained to the evaluators and their definitions were also inserted in the evaluation forms. The evaluators were trained with the scale and the sensory attributes used for the evaluation of biscuit samples (2 sessions × 2 h). As already published by Park et al. [49] the hardness was considered the force needed to bite through the sample by using the front teeth. Crispiness was evaluated as the force and the noise with which the sample breaks down between the molar teeth. Finally, the chewiness was evaluated as the energy necessary to masticate solid foods so that they can be easily swallowed.

### 2.2.10. Statistical Analysis

The results of three independent (*n* = 3) replicates were expressed as means ± standard deviations (SD). Data of proximate composition, sensory data and instrumental textural analysis were analyzed using Duncan multiple comparison test (*p* < 0.05) using the SPSS version 19 software (IBM Corp., Armonk, NY, USA). Correlation among means of the sensory data was determined using a two-tailed Pearson Correlation test (*p* < 0.05) using Microsoft Office—Excel.

#### **3. Results and Discussions**

#### *3.1. Proximate Composition of Flours*

The proximate composition of WF and RFSF is reported in Table 2. The data show that the two flours have complementary nutritional profiles. The moisture content of any flour is an important quality criterion for its preservation, packaging and transport as well. WF had eight times more humidity than RFSF (14.55% compared to 1.64%, respectively). The low moisture content for RFSF can be explained by the prior roasting process which removed most of the sample's water content. Comparison of the carbohydrate content of the two samples presented a similar pattern: WF presented high levels of carbohydrates (74.45%), whereas RFSF contained 21.76% of total carbohydrate. However, RFSF presented higher levels of protein (21.40%), fiber (8.75%) and fat content (42.50%) compared to WF.

**Table 2.** Proximate composition of raw materials.


\* Values represent mean of three independent determinations ± SD; Mean values followed by the same superscript alphabet in the row are not significantly different at *p* < 0.05 according to Duncan comparison test; fw-fresh weight.

Therefore, a composite flour can be successfully used to obtain biscuits with improved nutritional value. These results are in agreement with those obtained by Kaur et al. [26] and Kelapure [50] who found the fat content of flaxseed flour was 38.2 and 40.5%. The protein, crude fiber, and ash content of RFSF, in our study, was observed to be 21.40%, 8.75%, and 3.95%, respectively. These values correlated well with the values reported earlier by Hussain et al. [19], Kaur et al. [26], Masoodi [29] and Kelapure [50].

The valuable chemical composition of RFSF along with the high carbohydrate content of WF, especially starch, led to a composite flour with good characteristics for biscuit manufacturing. Mamat and Hill [51] showed that flour with high carbohydrate content and low in gluten is highly recommended for biscuit manufacturing. Therefore, we considered that the composite flours with 25% RFSF could be successfully used for further processing. WF contributes to the final characteristics of biscuits with the pasting properties of the starch and with the gluten content. Moreover, the high protein content of RFSF could contribute also to the pasting property on the finished product and to the dough viscosity, as it was reported previously in the development of protein-enriched composite flour for biscuits production [52].

#### *3.2. Volatile Compounds of Raw and Roasted Flaxseed*

The purpose of the analysis was to compare the volatile compounds profile of both raw and roasted flaxseed, to explain, based on the identified volatile compounds, consumers' acceptability of roasted seeds. As a result, a total number of 18 aroma compounds were identified by using ITEX/GS-MS and are presented in Table 3 group in six classes of compounds: alcohols, aldehydes, ketones, terpenes, and terpenoids, acids and others.


**Table 3.** Volatile compounds of raw flaxseeds and roasted flaxseed.

\* Each value was the mean of triplicate measurements; N.D.—not detected. \*\* drawn from [46,47]; Note: a,b different superscripts in a row indicate significant differences within samples (*p* < 0.05) according to Duncan comparison test.

> It was found that the main volatile compounds of raw flaxseed were hexan-1-ol (23.06%), acetophenone (13.22%), α-pinene (12.70%), D-limonene (10.72%) and on the other hand, the major volatile compounds in the roasted flaxseed were hexanal (24.24%), acetophenone (17.28%), benzahdehyde (10.42%), D-limonene (9.85%), α-pinene (6.81%), 3-methylbutan-1-ol (4.48%) and hexan-1-ol (3.74%), respectively (Table 3).

> Compounds with fresh and balsamic aroma characteristics, for example hexan-1 ol, benzophenone, β-pinene, D-limonene, camphene and benzoic acid, were present in significantly higher (*p* < 0.05) amounts in raw flaxseed compared to roasted flaxseed. With respect to hexan-1-ol, a lipid oxidation volatile compound with a significant value in raw flaxseed, its amount could be justified by the activity of dehydrogenase enzyme during storage [53].

> In the roasted flaxseed compounds with aromas like malt, burned sugar and almond were found in significantly higher amounts (*p* < 0.05) than in raw flaxseed. Hexanal is the primary oxidation product of linoleic acid [52]. The increase of hexanal in roasted flaxseed reaching a final value of 24.24% may be due to lipid oxidation during thermal treatment [54]. Roasted flaxseeds are a rich source of lipids and in the present study, a total amount of 42.50% total fat was previously mentioned. Furthermore, Wei et al. [53] reported a higher content of α-linolenic acid, the precursor of docosahexaenoic and eicosapentaenoic acids, in flaxseeds, thus explaining the formation of hexanal during the roasting process. Furthermore, acetotophenone (17.28%) was the major volatile compound from the ketone group, while the main alcohol identified was 3-methylbutan-1-ol (4.48%). The presence of aldehydes, ketones and alcohols in the roasted flaxseeds could be justified by thermal reactions during roasting such as non-enzymatic Maillard reactions and sugar caramelization. Likewise, the aforementioned compounds could also be formed as a result of lipid oxidation [54].
