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Functional cookies formulated with pistachio green hull extract; physicochemical, antioxidant, antidiabetic, sensory, and in vitro digestion properties

This study demonstrates that incorporating pistachio green hull extract into sugar-free cookies effectively enhances their antioxidant and antidiabetic properties while improving texture and maintaining sensory acceptability up to 4% concentration, making it a promising functional ingredient for glycemic control.

Original authors: Mohadese Mehrabiyana, Amin Karimi, Amir Pouya Ghandehari Yazdi, Reza Hajimohammadi-Farimani, Sepideh khorasani, Seid Mahdi Jafari

Published 2026-07-02

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Mohadese Mehrabiyana, Amin Karimi, Amir Pouya Ghandehari Yazdi, Reza Hajimohammadi-Farimani, Sepideh khorasani, Seid Mahdi Jafari

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the pistachio tree as a generous host. When we eat the nut, we usually throw away the green, leafy shell (the hull) that surrounds it. This paper treats that discarded shell not as trash, but as a hidden treasure chest full of powerful, natural compounds called polyphenols.

The researchers asked a simple question: What happens if we take this "trash" treasure, turn it into a powder, and bake it into a cookie?

Here is the story of what they found, explained simply:

1. The Mission: A "Super-Cookie"

Most cookies are like sugar bombs. They are made of refined flour and sugar, which act like a firework for your blood sugar, causing it to spike rapidly. The researchers wanted to build a "functional cookie"—a snack that tastes good but also acts like a shield against those blood sugar spikes. They used Pistachio Green Hull Extract (PGHE) as their secret weapon.

They baked four batches of cookies:

The Control: A normal, sugar-free cookie (no pistachio hull).
The Light, Medium, and Heavy: Cookies with 2%, 4%, and 6% pistachio hull powder added.

2. The "Shield" Effect (Antioxidants & Enzyme Blocking)

Think of your body's digestion as a factory line. Enzymes (like alpha-amylase and alpha-glucosidase) are the workers on that line, breaking down starch into sugar so your body can absorb it.

The Result: The pistachio hull extract acted like a traffic jam for these workers. The more hull powder in the cookie, the more the workers were slowed down.
The Evidence: The cookies with the most hull powder (6%) blocked nearly 70% of the starch-digesting enzyme and 63% of the sugar-digesting enzyme.
The Antioxidant Boost: The hull is also packed with "rust removers" (antioxidants). Adding the extract turned the cookie into a sponge for these compounds. The cookie with 6% extract had almost four times more antioxidant power than the plain cookie.

3. The "Digestion Test" (What happens in the stomach?)

The researchers didn't just guess; they simulated a human stomach and intestine in a lab dish.

The Control Cookie: When digested, it released a flood of sugar quickly.
The Pistachio Cookies: They released sugar much more slowly. The 6% cookie released 17.5% less sugar by the end of the digestion process.
The Takeaway: Even after being "digested," the pistachio cookies still held onto their antioxidant power, proving the compounds survived the stomach acid.

4. The Texture Change (The "Softening" Effect)

Usually, when you add dry powder to dough, you might expect the cookie to get hard and crumbly. Surprisingly, the opposite happened.

The Analogy: Imagine a tight, rigid brick wall (the normal cookie). The pistachio extract acted like a softener, loosening the bricks and creating tiny air pockets.
The Result: The cookies became significantly softer, less chewy, and less gummy. The 6% cookie was less than half as hard as the control cookie.
The Microscope View: Under a microscope, the normal cookie looked like a smooth, solid road. The pistachio cookies looked like a porous sponge with holes and cracks, which explains why they were softer.

5. The Taste Test (The "Goldilocks" Zone)

The researchers asked people to taste the cookies.

Appearance: The cookies got darker and redder (like a sunset) as more extract was added. People thought this looked fine.
Smell and Taste: This is where the limit was found.
- 2% and 4%: These tasted great. People couldn't tell much difference from the control, and they liked them.
- 6%: This was too much. The strong, earthy smell of the pistachio hull overpowered the cookie, and the taste became less pleasant.
The Verdict: The "sweet spot" is 4%. It offers the maximum health benefits (enzyme blocking and antioxidants) without ruining the flavor.

Summary

The paper concludes that pistachio hulls, usually thrown away, can be transformed into a powerful ingredient. By adding about 4% of this extract to sugar-free cookies, you create a snack that:

Is softer to eat.
Has supercharged antioxidants.
Slows down the release of sugar into your blood.
Tastes good to most people.

It's a way of turning agricultural waste into a "health shield" for your snack time.

Technical Summary: Functional Cookies Formulated with Pistachio Green Hull Extract

Problem Statement
Modern dietary patterns are increasingly dominated by processed foods rich in refined carbohydrates and added sugars, leading to postprandial hyperglycemia and a rising global prevalence of metabolic disorders such as type 2 diabetes. Conventional cookies, while popular, typically possess a high glycemic index (GI) due to their formulation with refined wheat flour and substantial sugar content. There is a critical need to develop functional bakery products that utilize natural bioactive compounds to attenuate postprandial hyperglycemia without compromising sensory quality. Pistachio green hull (PGH), a polyphenol-rich by-product of pistachio processing, represents an underutilized resource with proven antioxidant and enzyme-inhibiting properties, yet its application in sugar-free functional cookies requires further investigation regarding stability, digestibility, and consumer acceptance.

Methodology
This study formulated sugar-free functional cookies fortified with Pistachio Green Hull Extract (PGHE) at concentrations of 2%, 4%, and 6% (w/w), alongside a control sample without PGHE. The research employed a comprehensive analytical framework:

Physicochemical Analysis: Proximate composition (moisture, protein, fat, ash, carbohydrates) was determined using AOAC methods. Color parameters ( $L^*$ , $a^*$ , $b^*$ , $\Delta E$ ) were measured using a colorimeter.
Bioactivity Assessment: Total Phenolic Content (TPC) was quantified via the Folin–Ciocalteu method. Antioxidant activity (AxAc) was evaluated using DPPH radical scavenging assays.
Enzyme Inhibition: The inhibitory effects of cookie extracts on $\alpha$ -amylase (AA) and $\alpha$ -glucosidase (AG) were measured spectrophotometrically to assess potential antidiabetic mechanisms.
In Vitro Digestion: A simulated gastrointestinal digestion model (gastric followed by intestinal phases) was conducted to monitor the release of reducing sugars over 120 minutes and to evaluate the stability of antioxidant compounds post-digestion.
Textural and Microstructural Analysis: Texture Profile Analysis (TPA) measured hardness, cohesiveness, springiness, gumminess, and chewiness. Scanning Electron Microscopy (SEM) was used to examine the internal microstructure and starch-protein network integrity.
Sensory Evaluation: A panel of 25 trained participants rated the cookies on a 5-point hedonic scale for appearance, aroma, taste, color, texture, and overall acceptability.

Key Results

Physicochemical Properties: The addition of PGHE significantly increased the ash content (from 2.08% in control to 2.31% in 6% PGHE), indicating mineral enrichment, while moisture, protein, and fat contents remained statistically unchanged. Color analysis revealed a dose-dependent darkening of the cookies; $L^*$ values decreased from 52.11 (control) to 43.89 (6% PGHE), while redness ( $a^*$ ) and yellowness ( $b^*$ ) increased.
Bioactivity: TPC and antioxidant activity exhibited a strong dose-dependent increase. The 6% PGHE formulation achieved the highest TPC (16.70 mg GAE/g dw) and antioxidant activity (6.10 mmol Trolox eq/g dw), compared to 4.47 mg GAE/g dw and lower antioxidant values in the control. A high linear correlation ( $r=0.99$ ) was observed between TPC and antioxidant activity.
Enzyme Inhibition: PGHE incorporation significantly inhibited both AA and AG activities in a dose-dependent manner. The 6% formulation showed the strongest inhibition (70.29% for AA and 63.75% for AG). Strong correlations were found between TPC and enzyme inhibition ( $r=0.94$ for AA; $r=0.87$ for AG).
In Vitro Digestion: Simulated digestion confirmed that PGHE fortification reduced the release of reducing sugars, with the highest concentration (6%) reducing final sugar release by up to 17.5% compared to the control. Crucially, antioxidant activity was sustained and even enhanced in the digested samples, with the 6% formulation showing the highest post-digestion DPPH scavenging (6.10 µmol Trolox/g dw).
Texture and Microstructure: Textural analysis indicated that PGHE incorporation significantly reduced hardness, gumminess, and chewiness, resulting in softer cookies. SEM imaging revealed that while the control sample possessed a compact, continuous starch-protein network, PGHE-enriched samples displayed progressively disrupted, porous, and fragmented microstructures, particularly at the 6% level. This structural disruption is attributed to polyphenol-protein interactions that hinder gluten network formation.
Sensory Acceptability: Sensory scores for appearance and color remained acceptable across all treatments. However, aroma and taste scores declined significantly at the 6% concentration. Formulations containing up to 4% PGHE maintained good overall acceptability, whereas the 6% level negatively impacted flavor perception.

Significance and Claims
The paper concludes that PGHE is an effective functional ingredient for developing sugar-free cookies with enhanced bioactive properties. The study demonstrates that PGHE not only enriches the nutritional profile (increasing phenolics and minerals) but also imparts significant antidiabetic potential by inhibiting carbohydrate-digesting enzymes and reducing the glycemic response during simulated digestion. The authors claim that the bioactive compounds remain stable through baking and digestion, retaining their antioxidant capacity.

From a technological standpoint, the study highlights a trade-off: while PGHE improves functional properties and softens the texture, concentrations above 4% begin to compromise sensory attributes, specifically aroma and taste. Consequently, the authors posit that formulations containing up to 4% PGHE offer the optimal balance between health-promoting benefits and consumer acceptability. The research positions PGHE as a sustainable, value-added ingredient derived from agricultural waste, suitable for creating functional bakery products that support glycemic control and metabolic health. Future work suggested by the authors includes investigating in vivo glycemic responses, bioavailability, and shelf-life stability.