## Step 1: Define the symbolic representation of the problem
The problem involves two variables: 'sashimi' and 'fruit salads', which we can denote as $x_1$ and $x_2$ respectively. The objective function to minimize is $7x_1 + 7x_2$. The constraints are:
- $21x_1 + 3x_2 \geq 36$ (carbohydrates constraint)
- $10x_1 + 11x_2 \geq 57$ (umami index constraint)
- $8x_1 - 5x_2 \geq 0$ (sashimi and fruit salads mix constraint)
- $21x_1 + 3x_2 \leq 82$ (carbohydrates upper bound constraint)
- $10x_1 + 11x_2 \leq 71$ (umami index upper bound constraint)
- $x_1$ is an integer (sashimi is a nonfractional number)
- $x_2$ is a continuous variable (fruit salads can be a non-whole number)

## Step 2: Convert the problem into a Gurobi-compatible model
We will use Gurobi's Python API to model and solve this problem.

## 3: Write the Gurobi code
```python
import gurobi as gp

# Create a new model
m = gp.Model("optimization_problem")

# Define the variables
sashimi = m.addVar(name="sashimi", vtype=gp.GRB.INTEGER)  # integer variable
fruit_salads = m.addVar(name="fruit_salads")  # continuous variable

# Objective function: minimize 7 * sashimi + 7 * fruit_salads
m.setObjective(7 * sashimi + 7 * fruit_salads, gp.GRB.MINIMIZE)

# Constraints
m.addConstr(21 * sashimi + 3 * fruit_salads >= 36, name="carbohydrates_constraint")
m.addConstr(10 * sashimi + 11 * fruit_salads >= 57, name="umami_index_constraint")
m.addConstr(8 * sashimi - 5 * fruit_salads >= 0, name="sashimi_fruit_mix_constraint")
m.addConstr(21 * sashimi + 3 * fruit_salads <= 82, name="carbohydrates_upper_bound_constraint")
m.addConstr(10 * sashimi + 11 * fruit_salads <= 71, name="umami_index_upper_bound_constraint")

# Optimize the model
m.optimize()

# Print the solution
if m.status == gp.GRB.OPTIMAL:
    print("Optimal solution found.")
    print(f"Sashimi: {sashimi.varValue}")
    print(f"Fruit Salads: {fruit_salads.varValue}")
    print(f"Objective: {m.objVal}")
else:
    print("No optimal solution found.")
```

## 4: Provide the symbolic representation of the problem
```json
{
    'sym_variables': [('x1', 'sashimi'), ('x2', 'fruit salads')],
    'objective_function': '7*x1 + 7*x2',
    'constraints': [
        '21*x1 + 3*x2 >= 36',
        '10*x1 + 11*x2 >= 57',
        '8*x1 - 5*x2 >= 0',
        '21*x1 + 3*x2 <= 82',
        '10*x1 + 11*x2 <= 71',
        'x1 is an integer',
        'x2 is a continuous variable'
    ]
}
```